Merge branch 'MDL-44773-27' of git://github.com/FMCorz/moodle into MOODLE_27_STABLE

[moodle.git] / lib / markdown / Markdown.php

<?php
#
# Markdown  -  A text-to-HTML conversion tool for web writers
#
# PHP Markdown  
# Copyright (c) 2004-2013 Michel Fortin  
# <http://michelf.com/projects/php-markdown/>
#
# Original Markdown  
# Copyright (c) 2004-2006 John Gruber  
# <http://daringfireball.net/projects/markdown/>
#
namespace Michelf;


#
# Markdown Parser Class
#

class Markdown implements MarkdownInterface {

        ### Version ###

        const  MARKDOWNLIB_VERSION  =  "1.4.0";

        ### Simple Function Interface ###

        public static function defaultTransform($text) {
        #
        # Initialize the parser and return the result of its transform method.
        # This will work fine for derived classes too.
        #
                # Take parser class on which this function was called.
                $parser_class = \get_called_class();

                # try to take parser from the static parser list
                static $parser_list;
                $parser =& $parser_list[$parser_class];

                # create the parser it not already set
                if (!$parser)
                        $parser = new $parser_class;

                # Transform text using parser.
                return $parser->transform($text);
        }

        ### Configuration Variables ###

        # Change to ">" for HTML output.
        public $empty_element_suffix = " />";
        public $tab_width = 4;
        
        # Change to `true` to disallow markup or entities.
        public $no_markup = false;
        public $no_entities = false;
        
        # Predefined urls and titles for reference links and images.
        public $predef_urls = array();
        public $predef_titles = array();


        ### Parser Implementation ###

        # Regex to match balanced [brackets].
        # Needed to insert a maximum bracked depth while converting to PHP.
        protected $nested_brackets_depth = 6;
        protected $nested_brackets_re;
        
        protected $nested_url_parenthesis_depth = 4;
        protected $nested_url_parenthesis_re;

        # Table of hash values for escaped characters:
        protected $escape_chars = '\`*_{}[]()>#+-.!';
        protected $escape_chars_re;


        public function __construct() {
        #
        # Constructor function. Initialize appropriate member variables.
        #
                $this->_initDetab();
                $this->prepareItalicsAndBold();
        
                $this->nested_brackets_re = 
                        str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
                        str_repeat('\])*', $this->nested_brackets_depth);
        
                $this->nested_url_parenthesis_re = 
                        str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
                        str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);
                
                $this->escape_chars_re = '['.preg_quote($this->escape_chars).']';
                
                # Sort document, block, and span gamut in ascendent priority order.
                asort($this->document_gamut);
                asort($this->block_gamut);
                asort($this->span_gamut);
        }


        # Internal hashes used during transformation.
        protected $urls = array();
        protected $titles = array();
        protected $html_hashes = array();
        
        # Status flag to avoid invalid nesting.
        protected $in_anchor = false;
        
        
        protected function setup() {
        #
        # Called before the transformation process starts to setup parser 
        # states.
        #
                # Clear global hashes.
                $this->urls = $this->predef_urls;
                $this->titles = $this->predef_titles;
                $this->html_hashes = array();
                
                $this->in_anchor = false;
        }
        
        protected function teardown() {
        #
        # Called after the transformation process to clear any variable 
        # which may be taking up memory unnecessarly.
        #
                $this->urls = array();
                $this->titles = array();
                $this->html_hashes = array();
        }


        public function transform($text) {
        #
        # Main function. Performs some preprocessing on the input text
        # and pass it through the document gamut.
        #
                $this->setup();
        
                # Remove UTF-8 BOM and marker character in input, if present.
                $text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

                # Standardize line endings:
                #   DOS to Unix and Mac to Unix
                $text = preg_replace('{\r\n?}', "\n", $text);

                # Make sure $text ends with a couple of newlines:
                $text .= "\n\n";

                # Convert all tabs to spaces.
                $text = $this->detab($text);

                # Turn block-level HTML blocks into hash entries
                $text = $this->hashHTMLBlocks($text);

                # Strip any lines consisting only of spaces and tabs.
                # This makes subsequent regexen easier to write, because we can
                # match consecutive blank lines with /\n+/ instead of something
                # contorted like /[ ]*\n+/ .
                $text = preg_replace('/^[ ]+$/m', '', $text);

                # Run document gamut methods.
                foreach ($this->document_gamut as $method => $priority) {
                        $text = $this->$method($text);
                }
                
                $this->teardown();

                return $text . "\n";
        }
        
        protected $document_gamut = array(
                # Strip link definitions, store in hashes.
                "stripLinkDefinitions" => 20,
                
                "runBasicBlockGamut"   => 30,
                );


        protected function stripLinkDefinitions($text) {
        #
        # Strips link definitions from text, stores the URLs and titles in
        # hash references.
        #
                $less_than_tab = $this->tab_width - 1;

                # Link defs are in the form: ^[id]: url "optional title"
                $text = preg_replace_callback('{
                                                        ^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?: # id = $1
                                                          [ ]*
                                                          \n?                           # maybe *one* newline
                                                          [ ]*
                                                        (?:
                                                          <(.+?)>                       # url = $2
                                                        |
                                                          (\S+?)                        # url = $3
                                                        )
                                                          [ ]*
                                                          \n?                           # maybe one newline
                                                          [ ]*
                                                        (?:
                                                                (?<=\s)                 # lookbehind for whitespace
                                                                ["(]
                                                                (.*?)                   # title = $4
                                                                [")]
                                                                [ ]*
                                                        )?      # title is optional
                                                        (?:\n+|\Z)
                        }xm',
                        array(&$this, '_stripLinkDefinitions_callback'),
                        $text);
                return $text;
        }
        protected function _stripLinkDefinitions_callback($matches) {
                $link_id = strtolower($matches[1]);
                $url = $matches[2] == '' ? $matches[3] : $matches[2];
                $this->urls[$link_id] = $url;
                $this->titles[$link_id] =& $matches[4];
                return ''; # String that will replace the block
        }


        protected function hashHTMLBlocks($text) {
                if ($this->no_markup)  return $text;

                $less_than_tab = $this->tab_width - 1;

                # Hashify HTML blocks:
                # We only want to do this for block-level HTML tags, such as headers,
                # lists, and tables. That's because we still want to wrap <p>s around
                # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
                # phrase emphasis, and spans. The list of tags we're looking for is
                # hard-coded:
                #
                # *  List "a" is made of tags which can be both inline or block-level.
                #    These will be treated block-level when the start tag is alone on 
                #    its line, otherwise they're not matched here and will be taken as 
                #    inline later.
                # *  List "b" is made of tags which are always block-level;
                #
                $block_tags_a_re = 'ins|del';
                $block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
                                                   'script|noscript|form|fieldset|iframe|math|svg|'.
                                                   'article|section|nav|aside|hgroup|header|footer|'.
                                                   'figure';

                # Regular expression for the content of a block tag.
                $nested_tags_level = 4;
                $attr = '
                        (?>                             # optional tag attributes
                          \s                    # starts with whitespace
                          (?>
                                [^>"/]+         # text outside quotes
                          |
                                /+(?!>)         # slash not followed by ">"
                          |
                                "[^"]*"         # text inside double quotes (tolerate ">")
                          |
                                \'[^\']*\'      # text inside single quotes (tolerate ">")
                          )*
                        )?      
                        ';
                $content =
                        str_repeat('
                                (?>
                                  [^<]+                 # content without tag
                                |
                                  <\2                   # nested opening tag
                                        '.$attr.'       # attributes
                                        (?>
                                          />
                                        |
                                          >', $nested_tags_level).      # end of opening tag
                                          '.*?'.                                        # last level nested tag content
                        str_repeat('
                                          </\2\s*>      # closing nested tag
                                        )
                                  |                             
                                        <(?!/\2\s*>     # other tags with a different name
                                  )
                                )*',
                                $nested_tags_level);
                $content2 = str_replace('\2', '\3', $content);

                # First, look for nested blocks, e.g.:
                #       <div>
                #               <div>
                #               tags for inner block must be indented.
                #               </div>
                #       </div>
                #
                # The outermost tags must start at the left margin for this to match, and
                # the inner nested divs must be indented.
                # We need to do this before the next, more liberal match, because the next
                # match will start at the first `<div>` and stop at the first `</div>`.
                $text = preg_replace_callback('{(?>
                        (?>
                                (?<=\n\n)               # Starting after a blank line
                                |                               # or
                                \A\n?                   # the beginning of the doc
                        )
                        (                                               # save in $1

                          # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
                          # in between.
                                        
                                                [ ]{0,'.$less_than_tab.'}
                                                <('.$block_tags_b_re.')# start tag = $2
                                                '.$attr.'>                      # attributes followed by > and \n
                                                '.$content.'            # content, support nesting
                                                </\2>                           # the matching end tag
                                                [ ]*                            # trailing spaces/tabs
                                                (?=\n+|\Z)      # followed by a newline or end of document

                        | # Special version for tags of group a.

                                                [ ]{0,'.$less_than_tab.'}
                                                <('.$block_tags_a_re.')# start tag = $3
                                                '.$attr.'>[ ]*\n        # attributes followed by >
                                                '.$content2.'           # content, support nesting
                                                </\3>                           # the matching end tag
                                                [ ]*                            # trailing spaces/tabs
                                                (?=\n+|\Z)      # followed by a newline or end of document
                                        
                        | # Special case just for <hr />. It was easier to make a special 
                          # case than to make the other regex more complicated.
                        
                                                [ ]{0,'.$less_than_tab.'}
                                                <(hr)                           # start tag = $2
                                                '.$attr.'                       # attributes
                                                /?>                                     # the matching end tag
                                                [ ]*
                                                (?=\n{2,}|\Z)           # followed by a blank line or end of document
                        
                        | # Special case for standalone HTML comments:
                        
                                        [ ]{0,'.$less_than_tab.'}
                                        (?s:
                                                <!-- .*? -->
                                        )
                                        [ ]*
                                        (?=\n{2,}|\Z)           # followed by a blank line or end of document
                        
                        | # PHP and ASP-style processor instructions (<? and <%)
                        
                                        [ ]{0,'.$less_than_tab.'}
                                        (?s:
                                                <([?%])                 # $2
                                                .*?
                                                \2>
                                        )
                                        [ ]*
                                        (?=\n{2,}|\Z)           # followed by a blank line or end of document
                                        
                        )
                        )}Sxmi',
                        array(&$this, '_hashHTMLBlocks_callback'),
                        $text);

                return $text;
        }
        protected function _hashHTMLBlocks_callback($matches) {
                $text = $matches[1];
                $key  = $this->hashBlock($text);
                return "\n\n$key\n\n";
        }
        
        
        protected function hashPart($text, $boundary = 'X') {
        #
        # Called whenever a tag must be hashed when a function insert an atomic 
        # element in the text stream. Passing $text to through this function gives
        # a unique text-token which will be reverted back when calling unhash.
        #
        # The $boundary argument specify what character should be used to surround
        # the token. By convension, "B" is used for block elements that needs not
        # to be wrapped into paragraph tags at the end, ":" is used for elements
        # that are word separators and "X" is used in the general case.
        #
                # Swap back any tag hash found in $text so we do not have to `unhash`
                # multiple times at the end.
                $text = $this->unhash($text);
                
                # Then hash the block.
                static $i = 0;
                $key = "$boundary\x1A" . ++$i . $boundary;
                $this->html_hashes[$key] = $text;
                return $key; # String that will replace the tag.
        }


        protected function hashBlock($text) {
        #
        # Shortcut function for hashPart with block-level boundaries.
        #
                return $this->hashPart($text, 'B');
        }


        protected $block_gamut = array(
        #
        # These are all the transformations that form block-level
        # tags like paragraphs, headers, and list items.
        #
                "doHeaders"         => 10,
                "doHorizontalRules" => 20,
                
                "doLists"           => 40,
                "doCodeBlocks"      => 50,
                "doBlockQuotes"     => 60,
                );

        protected function runBlockGamut($text) {
        #
        # Run block gamut tranformations.
        #
                # We need to escape raw HTML in Markdown source before doing anything 
                # else. This need to be done for each block, and not only at the 
                # begining in the Markdown function since hashed blocks can be part of
                # list items and could have been indented. Indented blocks would have 
                # been seen as a code block in a previous pass of hashHTMLBlocks.
                $text = $this->hashHTMLBlocks($text);
                
                return $this->runBasicBlockGamut($text);
        }
        
        protected function runBasicBlockGamut($text) {
        #
        # Run block gamut tranformations, without hashing HTML blocks. This is 
        # useful when HTML blocks are known to be already hashed, like in the first
        # whole-document pass.
        #
                foreach ($this->block_gamut as $method => $priority) {
                        $text = $this->$method($text);
                }
                
                # Finally form paragraph and restore hashed blocks.
                $text = $this->formParagraphs($text);

                return $text;
        }
        
        
        protected function doHorizontalRules($text) {
                # Do Horizontal Rules:
                return preg_replace(
                        '{
                                ^[ ]{0,3}       # Leading space
                                ([-*_])         # $1: First marker
                                (?>                     # Repeated marker group
                                        [ ]{0,2}        # Zero, one, or two spaces.
                                        \1                      # Marker character
                                ){2,}           # Group repeated at least twice
                                [ ]*            # Tailing spaces
                                $                       # End of line.
                        }mx',
                        "\n".$this->hashBlock("<hr$this->empty_element_suffix")."\n", 
                        $text);
        }


        protected $span_gamut = array(
        #
        # These are all the transformations that occur *within* block-level
        # tags like paragraphs, headers, and list items.
        #
                # Process character escapes, code spans, and inline HTML
                # in one shot.
                "parseSpan"           => -30,

                # Process anchor and image tags. Images must come first,
                # because ![foo][f] looks like an anchor.
                "doImages"            =>  10,
                "doAnchors"           =>  20,
                
                # Make links out of things like `<http://example.com/>`
                # Must come after doAnchors, because you can use < and >
                # delimiters in inline links like [this](<url>).
                "doAutoLinks"         =>  30,
                "encodeAmpsAndAngles" =>  40,

                "doItalicsAndBold"    =>  50,
                "doHardBreaks"        =>  60,
                );

        protected function runSpanGamut($text) {
        #
        # Run span gamut tranformations.
        #
                foreach ($this->span_gamut as $method => $priority) {
                        $text = $this->$method($text);
                }

                return $text;
        }
        
        
        protected function doHardBreaks($text) {
                # Do hard breaks:
                return preg_replace_callback('/ {2,}\n/', 
                        array(&$this, '_doHardBreaks_callback'), $text);
        }
        protected function _doHardBreaks_callback($matches) {
                return $this->hashPart("<br$this->empty_element_suffix\n");
        }


        protected function doAnchors($text) {
        #
        # Turn Markdown link shortcuts into XHTML <a> tags.
        #
                if ($this->in_anchor) return $text;
                $this->in_anchor = true;
                
                #
                # First, handle reference-style links: [link text] [id]
                #
                $text = preg_replace_callback('{
                        (                                       # wrap whole match in $1
                          \[
                                ('.$this->nested_brackets_re.') # link text = $2
                          \]

                          [ ]?                          # one optional space
                          (?:\n[ ]*)?           # one optional newline followed by spaces

                          \[
                                (.*?)           # id = $3
                          \]
                        )
                        }xs',
                        array(&$this, '_doAnchors_reference_callback'), $text);

                #
                # Next, inline-style links: [link text](url "optional title")
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          \[
                                ('.$this->nested_brackets_re.') # link text = $2
                          \]
                          \(                    # literal paren
                                [ \n]*
                                (?:
                                        <(.+?)> # href = $3
                                |
                                        ('.$this->nested_url_parenthesis_re.')  # href = $4
                                )
                                [ \n]*
                                (                       # $5
                                  ([\'"])       # quote char = $6
                                  (.*?)         # Title = $7
                                  \6            # matching quote
                                  [ \n]*        # ignore any spaces/tabs between closing quote and )
                                )?                      # title is optional
                          \)
                        )
                        }xs',
                        array(&$this, '_doAnchors_inline_callback'), $text);

                #
                # Last, handle reference-style shortcuts: [link text]
                # These must come last in case you've also got [link text][1]
                # or [link text](/foo)
                #
                $text = preg_replace_callback('{
                        (                                       # wrap whole match in $1
                          \[
                                ([^\[\]]+)              # link text = $2; can\'t contain [ or ]
                          \]
                        )
                        }xs',
                        array(&$this, '_doAnchors_reference_callback'), $text);

                $this->in_anchor = false;
                return $text;
        }
        protected function _doAnchors_reference_callback($matches) {
                $whole_match =  $matches[1];
                $link_text   =  $matches[2];
                $link_id     =& $matches[3];

                if ($link_id == "") {
                        # for shortcut links like [this][] or [this].
                        $link_id = $link_text;
                }
                
                # lower-case and turn embedded newlines into spaces
                $link_id = strtolower($link_id);
                $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

                if (isset($this->urls[$link_id])) {
                        $url = $this->urls[$link_id];
                        $url = $this->encodeAttribute($url);
                        
                        $result = "<a href=\"$url\"";
                        if ( isset( $this->titles[$link_id] ) ) {
                                $title = $this->titles[$link_id];
                                $title = $this->encodeAttribute($title);
                                $result .=  " title=\"$title\"";
                        }
                
                        $link_text = $this->runSpanGamut($link_text);
                        $result .= ">$link_text</a>";
                        $result = $this->hashPart($result);
                }
                else {
                        $result = $whole_match;
                }
                return $result;
        }
        protected function _doAnchors_inline_callback($matches) {
                $whole_match    =  $matches[1];
                $link_text              =  $this->runSpanGamut($matches[2]);
                $url                    =  $matches[3] == '' ? $matches[4] : $matches[3];
                $title                  =& $matches[7];

                $url = $this->encodeAttribute($url);

                $result = "<a href=\"$url\"";
                if (isset($title)) {
                        $title = $this->encodeAttribute($title);
                        $result .=  " title=\"$title\"";
                }
                
                $link_text = $this->runSpanGamut($link_text);
                $result .= ">$link_text</a>";

                return $this->hashPart($result);
        }


        protected function doImages($text) {
        #
        # Turn Markdown image shortcuts into <img> tags.
        #
                #
                # First, handle reference-style labeled images: ![alt text][id]
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          !\[
                                ('.$this->nested_brackets_re.')         # alt text = $2
                          \]

                          [ ]?                          # one optional space
                          (?:\n[ ]*)?           # one optional newline followed by spaces

                          \[
                                (.*?)           # id = $3
                          \]

                        )
                        }xs', 
                        array(&$this, '_doImages_reference_callback'), $text);

                #
                # Next, handle inline images:  ![alt text](url "optional title")
                # Don't forget: encode * and _
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          !\[
                                ('.$this->nested_brackets_re.')         # alt text = $2
                          \]
                          \s?                   # One optional whitespace character
                          \(                    # literal paren
                                [ \n]*
                                (?:
                                        <(\S*)> # src url = $3
                                |
                                        ('.$this->nested_url_parenthesis_re.')  # src url = $4
                                )
                                [ \n]*
                                (                       # $5
                                  ([\'"])       # quote char = $6
                                  (.*?)         # title = $7
                                  \6            # matching quote
                                  [ \n]*
                                )?                      # title is optional
                          \)
                        )
                        }xs',
                        array(&$this, '_doImages_inline_callback'), $text);

                return $text;
        }
        protected function _doImages_reference_callback($matches) {
                $whole_match = $matches[1];
                $alt_text    = $matches[2];
                $link_id     = strtolower($matches[3]);

                if ($link_id == "") {
                        $link_id = strtolower($alt_text); # for shortcut links like ![this][].
                }

                $alt_text = $this->encodeAttribute($alt_text);
                if (isset($this->urls[$link_id])) {
                        $url = $this->encodeAttribute($this->urls[$link_id]);
                        $result = "<img src=\"$url\" alt=\"$alt_text\"";
                        if (isset($this->titles[$link_id])) {
                                $title = $this->titles[$link_id];
                                $title = $this->encodeAttribute($title);
                                $result .=  " title=\"$title\"";
                        }
                        $result .= $this->empty_element_suffix;
                        $result = $this->hashPart($result);
                }
                else {
                        # If there's no such link ID, leave intact:
                        $result = $whole_match;
                }

                return $result;
        }
        protected function _doImages_inline_callback($matches) {
                $whole_match    = $matches[1];
                $alt_text               = $matches[2];
                $url                    = $matches[3] == '' ? $matches[4] : $matches[3];
                $title                  =& $matches[7];

                $alt_text = $this->encodeAttribute($alt_text);
                $url = $this->encodeAttribute($url);
                $result = "<img src=\"$url\" alt=\"$alt_text\"";
                if (isset($title)) {
                        $title = $this->encodeAttribute($title);
                        $result .=  " title=\"$title\""; # $title already quoted
                }
                $result .= $this->empty_element_suffix;

                return $this->hashPart($result);
        }


        protected function doHeaders($text) {
                # Setext-style headers:
                #         Header 1
                #         ========
                #  
                #         Header 2
                #         --------
                #
                $text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
                        array(&$this, '_doHeaders_callback_setext'), $text);

                # atx-style headers:
                #       # Header 1
                #       ## Header 2
                #       ## Header 2 with closing hashes ##
                #       ...
                #       ###### Header 6
                #
                $text = preg_replace_callback('{
                                ^(\#{1,6})      # $1 = string of #\'s
                                [ ]*
                                (.+?)           # $2 = Header text
                                [ ]*
                                \#*                     # optional closing #\'s (not counted)
                                \n+
                        }xm',
                        array(&$this, '_doHeaders_callback_atx'), $text);

                return $text;
        }
        protected function _doHeaders_callback_setext($matches) {
                # Terrible hack to check we haven't found an empty list item.
                if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
                        return $matches[0];
                
                $level = $matches[2]{0} == '=' ? 1 : 2;
                $block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";
                return "\n" . $this->hashBlock($block) . "\n\n";
        }
        protected function _doHeaders_callback_atx($matches) {
                $level = strlen($matches[1]);
                $block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";
                return "\n" . $this->hashBlock($block) . "\n\n";
        }


        protected function doLists($text) {
        #
        # Form HTML ordered (numbered) and unordered (bulleted) lists.
        #
                $less_than_tab = $this->tab_width - 1;

                # Re-usable patterns to match list item bullets and number markers:
                $marker_ul_re  = '[*+-]';
                $marker_ol_re  = '\d+[\.]';
                $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

                $markers_relist = array(
                        $marker_ul_re => $marker_ol_re,
                        $marker_ol_re => $marker_ul_re,
                        );

                foreach ($markers_relist as $marker_re => $other_marker_re) {
                        # Re-usable pattern to match any entirel ul or ol list:
                        $whole_list_re = '
                                (                                                               # $1 = whole list
                                  (                                                             # $2
                                        ([ ]{0,'.$less_than_tab.'})     # $3 = number of spaces
                                        ('.$marker_re.')                        # $4 = first list item marker
                                        [ ]+
                                  )
                                  (?s:.+?)
                                  (                                                             # $5
                                          \z
                                        |
                                          \n{2,}
                                          (?=\S)
                                          (?!                                           # Negative lookahead for another list item marker
                                                [ ]*
                                                '.$marker_re.'[ ]+
                                          )
                                        |
                                          (?=                                           # Lookahead for another kind of list
                                            \n
                                                \3                                              # Must have the same indentation
                                                '.$other_marker_re.'[ ]+
                                          )
                                  )
                                )
                        '; // mx
                        
                        # We use a different prefix before nested lists than top-level lists.
                        # See extended comment in _ProcessListItems().
                
                        if ($this->list_level) {
                                $text = preg_replace_callback('{
                                                ^
                                                '.$whole_list_re.'
                                        }mx',
                                        array(&$this, '_doLists_callback'), $text);
                        }
                        else {
                                $text = preg_replace_callback('{
                                                (?:(?<=\n)\n|\A\n?) # Must eat the newline
                                                '.$whole_list_re.'
                                        }mx',
                                        array(&$this, '_doLists_callback'), $text);
                        }
                }

                return $text;
        }
        protected function _doLists_callback($matches) {
                # Re-usable patterns to match list item bullets and number markers:
                $marker_ul_re  = '[*+-]';
                $marker_ol_re  = '\d+[\.]';
                $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";
                
                $list = $matches[1];
                $list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";
                
                $marker_any_re = ( $list_type == "ul" ? $marker_ul_re : $marker_ol_re );
                
                $list .= "\n";
                $result = $this->processListItems($list, $marker_any_re);
                
                $result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");
                return "\n". $result ."\n\n";
        }

        protected $list_level = 0;

        protected function processListItems($list_str, $marker_any_re) {
        #
        #       Process the contents of a single ordered or unordered list, splitting it
        #       into individual list items.
        #
                # The $this->list_level global keeps track of when we're inside a list.
                # Each time we enter a list, we increment it; when we leave a list,
                # we decrement. If it's zero, we're not in a list anymore.
                #
                # We do this because when we're not inside a list, we want to treat
                # something like this:
                #
                #               I recommend upgrading to version
                #               8. Oops, now this line is treated
                #               as a sub-list.
                #
                # As a single paragraph, despite the fact that the second line starts
                # with a digit-period-space sequence.
                #
                # Whereas when we're inside a list (or sub-list), that line will be
                # treated as the start of a sub-list. What a kludge, huh? This is
                # an aspect of Markdown's syntax that's hard to parse perfectly
                # without resorting to mind-reading. Perhaps the solution is to
                # change the syntax rules such that sub-lists must start with a
                # starting cardinal number; e.g. "1." or "a.".
                
                $this->list_level++;

                # trim trailing blank lines:
                $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

                $list_str = preg_replace_callback('{
                        (\n)?                                                   # leading line = $1
                        (^[ ]*)                                                 # leading whitespace = $2
                        ('.$marker_any_re.'                             # list marker and space = $3
                                (?:[ ]+|(?=\n)) # space only required if item is not empty
                        )
                        ((?s:.*?))                                              # list item text   = $4
                        (?:(\n+(?=\n))|\n)                              # tailing blank line = $5
                        (?= \n* (\z | \2 ('.$marker_any_re.') (?:[ ]+|(?=\n))))
                        }xm',
                        array(&$this, '_processListItems_callback'), $list_str);

                $this->list_level--;
                return $list_str;
        }
        protected function _processListItems_callback($matches) {
                $item = $matches[4];
                $leading_line =& $matches[1];
                $leading_space =& $matches[2];
                $marker_space = $matches[3];
                $tailing_blank_line =& $matches[5];

                if ($leading_line || $tailing_blank_line || 
                        preg_match('/\n{2,}/', $item))
                {
                        # Replace marker with the appropriate whitespace indentation
                        $item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
                        $item = $this->runBlockGamut($this->outdent($item)."\n");
                }
                else {
                        # Recursion for sub-lists:
                        $item = $this->doLists($this->outdent($item));
                        $item = preg_replace('/\n+$/', '', $item);
                        $item = $this->runSpanGamut($item);
                }

                return "<li>" . $item . "</li>\n";
        }


        protected function doCodeBlocks($text) {
        #
        #       Process Markdown `<pre><code>` blocks.
        #
                $text = preg_replace_callback('{
                                (?:\n\n|\A\n?)
                                (                   # $1 = the code block -- one or more lines, starting with a space/tab
                                  (?>
                                        [ ]{'.$this->tab_width.'}  # Lines must start with a tab or a tab-width of spaces
                                        .*\n+
                                  )+
                                )
                                ((?=^[ ]{0,'.$this->tab_width.'}\S)|\Z) # Lookahead for non-space at line-start, or end of doc
                        }xm',
                        array(&$this, '_doCodeBlocks_callback'), $text);

                return $text;
        }
        protected function _doCodeBlocks_callback($matches) {
                $codeblock = $matches[1];

                $codeblock = $this->outdent($codeblock);
                $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

                # trim leading newlines and trailing newlines
                $codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

                $codeblock = "<pre><code>$codeblock\n</code></pre>";
                return "\n\n".$this->hashBlock($codeblock)."\n\n";
        }


        protected function makeCodeSpan($code) {
        #
        # Create a code span markup for $code. Called from handleSpanToken.
        #
                $code = htmlspecialchars(trim($code), ENT_NOQUOTES);
                return $this->hashPart("<code>$code</code>");
        }


        protected $em_relist = array(
                ''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?=\S|$)(?![\.,:;]\s)',
                '*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
                '_' => '(?<=\S|^)(?<!_)_(?!_)',
                );
        protected $strong_relist = array(
                ''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?=\S|$)(?![\.,:;]\s)',
                '**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
                '__' => '(?<=\S|^)(?<!_)__(?!_)',
                );
        protected $em_strong_relist = array(
                ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?=\S|$)(?![\.,:;]\s)',
                '***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
                '___' => '(?<=\S|^)(?<!_)___(?!_)',
                );
        protected $em_strong_prepared_relist;
        
        protected function prepareItalicsAndBold() {
        #
        # Prepare regular expressions for searching emphasis tokens in any
        # context.
        #
                foreach ($this->em_relist as $em => $em_re) {
                        foreach ($this->strong_relist as $strong => $strong_re) {
                                # Construct list of allowed token expressions.
                                $token_relist = array();
                                if (isset($this->em_strong_relist["$em$strong"])) {
                                        $token_relist[] = $this->em_strong_relist["$em$strong"];
                                }
                                $token_relist[] = $em_re;
                                $token_relist[] = $strong_re;
                                
                                # Construct master expression from list.
                                $token_re = '{('. implode('|', $token_relist) .')}';
                                $this->em_strong_prepared_relist["$em$strong"] = $token_re;
                        }
                }
        }
        
        protected function doItalicsAndBold($text) {
                $token_stack = array('');
                $text_stack = array('');
                $em = '';
                $strong = '';
                $tree_char_em = false;
                
                while (1) {
                        #
                        # Get prepared regular expression for seraching emphasis tokens
                        # in current context.
                        #
                        $token_re = $this->em_strong_prepared_relist["$em$strong"];
                        
                        #
                        # Each loop iteration search for the next emphasis token. 
                        # Each token is then passed to handleSpanToken.
                        #
                        $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
                        $text_stack[0] .= $parts[0];
                        $token =& $parts[1];
                        $text =& $parts[2];
                        
                        if (empty($token)) {
                                # Reached end of text span: empty stack without emitting.
                                # any more emphasis.
                                while ($token_stack[0]) {
                                        $text_stack[1] .= array_shift($token_stack);
                                        $text_stack[0] .= array_shift($text_stack);
                                }
                                break;
                        }
                        
                        $token_len = strlen($token);
                        if ($tree_char_em) {
                                # Reached closing marker while inside a three-char emphasis.
                                if ($token_len == 3) {
                                        # Three-char closing marker, close em and strong.
                                        array_shift($token_stack);
                                        $span = array_shift($text_stack);
                                        $span = $this->runSpanGamut($span);
                                        $span = "<strong><em>$span</em></strong>";
                                        $text_stack[0] .= $this->hashPart($span);
                                        $em = '';
                                        $strong = '';
                                } else {
                                        # Other closing marker: close one em or strong and
                                        # change current token state to match the other
                                        $token_stack[0] = str_repeat($token{0}, 3-$token_len);
                                        $tag = $token_len == 2 ? "strong" : "em";
                                        $span = $text_stack[0];
                                        $span = $this->runSpanGamut($span);
                                        $span = "<$tag>$span</$tag>";
                                        $text_stack[0] = $this->hashPart($span);
                                        $$tag = ''; # $$tag stands for $em or $strong
                                }
                                $tree_char_em = false;
                        } else if ($token_len == 3) {
                                if ($em) {
                                        # Reached closing marker for both em and strong.
                                        # Closing strong marker:
                                        for ($i = 0; $i < 2; ++$i) {
                                                $shifted_token = array_shift($token_stack);
                                                $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                                                $span = array_shift($text_stack);
                                                $span = $this->runSpanGamut($span);
                                                $span = "<$tag>$span</$tag>";
                                                $text_stack[0] .= $this->hashPart($span);
                                                $$tag = ''; # $$tag stands for $em or $strong
                                        }
                                } else {
                                        # Reached opening three-char emphasis marker. Push on token 
                                        # stack; will be handled by the special condition above.
                                        $em = $token{0};
                                        $strong = "$em$em";
                                        array_unshift($token_stack, $token);
                                        array_unshift($text_stack, '');
                                        $tree_char_em = true;
                                }
                        } else if ($token_len == 2) {
                                if ($strong) {
                                        # Unwind any dangling emphasis marker:
                                        if (strlen($token_stack[0]) == 1) {
                                                $text_stack[1] .= array_shift($token_stack);
                                                $text_stack[0] .= array_shift($text_stack);
                                        }
                                        # Closing strong marker:
                                        array_shift($token_stack);
                                        $span = array_shift($text_stack);
                                        $span = $this->runSpanGamut($span);
                                        $span = "<strong>$span</strong>";
                                        $text_stack[0] .= $this->hashPart($span);
                                        $strong = '';
                                } else {
                                        array_unshift($token_stack, $token);
                                        array_unshift($text_stack, '');
                                        $strong = $token;
                                }
                        } else {
                                # Here $token_len == 1
                                if ($em) {
                                        if (strlen($token_stack[0]) == 1) {
                                                # Closing emphasis marker:
                                                array_shift($token_stack);
                                                $span = array_shift($text_stack);
                                                $span = $this->runSpanGamut($span);
                                                $span = "<em>$span</em>";
                                                $text_stack[0] .= $this->hashPart($span);
                                                $em = '';
                                        } else {
                                                $text_stack[0] .= $token;
                                        }
                                } else {
                                        array_unshift($token_stack, $token);
                                        array_unshift($text_stack, '');
                                        $em = $token;
                                }
                        }
                }
                return $text_stack[0];
        }


        protected function doBlockQuotes($text) {
                $text = preg_replace_callback('/
                          (                                                             # Wrap whole match in $1
                                (?>
                                  ^[ ]*>[ ]?                    # ">" at the start of a line
                                        .+\n                                    # rest of the first line
                                  (.+\n)*                                       # subsequent consecutive lines
                                  \n*                                           # blanks
                                )+
                          )
                        /xm',
                        array(&$this, '_doBlockQuotes_callback'), $text);

                return $text;
        }
        protected function _doBlockQuotes_callback($matches) {
                $bq = $matches[1];
                # trim one level of quoting - trim whitespace-only lines
                $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
                $bq = $this->runBlockGamut($bq);                # recurse

                $bq = preg_replace('/^/m', "  ", $bq);
                # These leading spaces cause problem with <pre> content, 
                # so we need to fix that:
                $bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
                        array(&$this, '_doBlockQuotes_callback2'), $bq);

                return "\n". $this->hashBlock("<blockquote>\n$bq\n</blockquote>")."\n\n";
        }
        protected function _doBlockQuotes_callback2($matches) {
                $pre = $matches[1];
                $pre = preg_replace('/^  /m', '', $pre);
                return $pre;
        }


        protected function formParagraphs($text) {
        #
        #       Params:
        #               $text - string to process with html <p> tags
        #
                # Strip leading and trailing lines:
                $text = preg_replace('/\A\n+|\n+\z/', '', $text);

                $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

                #
                # Wrap <p> tags and unhashify HTML blocks
                #
                foreach ($grafs as $key => $value) {
                        if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
                                # Is a paragraph.
                                $value = $this->runSpanGamut($value);
                                $value = preg_replace('/^([ ]*)/', "<p>", $value);
                                $value .= "</p>";
                                $grafs[$key] = $this->unhash($value);
                        }
                        else {
                                # Is a block.
                                # Modify elements of @grafs in-place...
                                $graf = $value;
                                $block = $this->html_hashes[$graf];
                                $graf = $block;
//                              if (preg_match('{
//                                      \A
//                                      (                                                       # $1 = <div> tag
//                                        <div  \s+
//                                        [^>]*
//                                        \b
//                                        markdown\s*=\s*  ([\'"])      #       $2 = attr quote char
//                                        1
//                                        \2
//                                        [^>]*
//                                        >
//                                      )
//                                      (                                                       # $3 = contents
//                                      .*
//                                      )
//                                      (</div>)                                        # $4 = closing tag
//                                      \z
//                                      }xs', $block, $matches))
//                              {
//                                      list(, $div_open, , $div_content, $div_close) = $matches;
//
//                                      # We can't call Markdown(), because that resets the hash;
//                                      # that initialization code should be pulled into its own sub, though.
//                                      $div_content = $this->hashHTMLBlocks($div_content);
//                                      
//                                      # Run document gamut methods on the content.
//                                      foreach ($this->document_gamut as $method => $priority) {
//                                              $div_content = $this->$method($div_content);
//                                      }
//
//                                      $div_open = preg_replace(
//                                              '{\smarkdown\s*=\s*([\'"]).+?\1}', '', $div_open);
//
//                                      $graf = $div_open . "\n" . $div_content . "\n" . $div_close;
//                              }
                                $grafs[$key] = $graf;
                        }
                }

                return implode("\n\n", $grafs);
        }


        protected function encodeAttribute($text) {
        #
        # Encode text for a double-quoted HTML attribute. This function
        # is *not* suitable for attributes enclosed in single quotes.
        #
                $text = $this->encodeAmpsAndAngles($text);
                $text = str_replace('"', '&quot;', $text);
                return $text;
        }
        
        
        protected function encodeAmpsAndAngles($text) {
        #
        # Smart processing for ampersands and angle brackets that need to 
        # be encoded. Valid character entities are left alone unless the
        # no-entities mode is set.
        #
                if ($this->no_entities) {
                        $text = str_replace('&', '&amp;', $text);
                } else {
                        # Ampersand-encoding based entirely on Nat Irons's Amputator
                        # MT plugin: <http://bumppo.net/projects/amputator/>
                        $text = preg_replace('/&(?!#?[xX]?(?:[0-9a-fA-F]+|\w+);)/', 
                                                                '&amp;', $text);
                }
                # Encode remaining <'s
                $text = str_replace('<', '&lt;', $text);

                return $text;
        }


        protected function doAutoLinks($text) {
                $text = preg_replace_callback('{<((https?|ftp|dict):[^\'">\s]+)>}i', 
                        array(&$this, '_doAutoLinks_url_callback'), $text);

                # Email addresses: <address@domain.foo>
                $text = preg_replace_callback('{
                        <
                        (?:mailto:)?
                        (
                                (?:
                                        [-!#$%&\'*+/=?^_`.{|}~\w\x80-\xFF]+
                                |
                                        ".*?"
                                )
                                \@
                                (?:
                                        [-a-z0-9\x80-\xFF]+(\.[-a-z0-9\x80-\xFF]+)*\.[a-z]+
                                |
                                        \[[\d.a-fA-F:]+\]       # IPv4 & IPv6
                                )
                        )
                        >
                        }xi',
                        array(&$this, '_doAutoLinks_email_callback'), $text);
                $text = preg_replace_callback('{<(tel:([^\'">\s]+))>}i',array(&$this, '_doAutoLinks_tel_callback'), $text);

                return $text;
        }
        protected function _doAutoLinks_tel_callback($matches) {
                $url = $this->encodeAttribute($matches[1]);
                $tel = $this->encodeAttribute($matches[2]);
                $link = "<a href=\"$url\">$tel</a>";
                return $this->hashPart($link);
        }
        protected function _doAutoLinks_url_callback($matches) {
                $url = $this->encodeAttribute($matches[1]);
                $link = "<a href=\"$url\">$url</a>";
                return $this->hashPart($link);
        }
        protected function _doAutoLinks_email_callback($matches) {
                $address = $matches[1];
                $link = $this->encodeEmailAddress($address);
                return $this->hashPart($link);
        }


        protected function encodeEmailAddress($addr) {
        #
        #       Input: an email address, e.g. "foo@example.com"
        #
        #       Output: the email address as a mailto link, with each character
        #               of the address encoded as either a decimal or hex entity, in
        #               the hopes of foiling most address harvesting spam bots. E.g.:
        #
        #         <p><a href="&#109;&#x61;&#105;&#x6c;&#116;&#x6f;&#58;&#x66;o&#111;
        #        &#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;&#101;&#46;&#x63;&#111;
        #        &#x6d;">&#x66;o&#111;&#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;
        #        &#101;&#46;&#x63;&#111;&#x6d;</a></p>
        #
        #       Based by a filter by Matthew Wickline, posted to BBEdit-Talk.
        #   With some optimizations by Milian Wolff.
        #
                $addr = "mailto:" . $addr;
                $chars = preg_split('/(?<!^)(?!$)/', $addr);
                $seed = (int)abs(crc32($addr) / strlen($addr)); # Deterministic seed.
                
                foreach ($chars as $key => $char) {
                        $ord = ord($char);
                        # Ignore non-ascii chars.
                        if ($ord < 128) {
                                $r = ($seed * (1 + $key)) % 100; # Pseudo-random function.
                                # roughly 10% raw, 45% hex, 45% dec
                                # '@' *must* be encoded. I insist.
                                if ($r > 90 && $char != '@') /* do nothing */;
                                else if ($r < 45) $chars[$key] = '&#x'.dechex($ord).';';
                                else              $chars[$key] = '&#'.$ord.';';
                        }
                }
                
                $addr = implode('', $chars);
                $text = implode('', array_slice($chars, 7)); # text without `mailto:`
                $addr = "<a href=\"$addr\">$text</a>";

                return $addr;
        }


        protected function parseSpan($str) {
        #
        # Take the string $str and parse it into tokens, hashing embeded HTML,
        # escaped characters and handling code spans.
        #
                $output = '';
                
                $span_re = '{
                                (
                                        \\\\'.$this->escape_chars_re.'
                                |
                                        (?<![`\\\\])
                                        `+                                              # code span marker
                        '.( $this->no_markup ? '' : '
                                |
                                        <!--    .*?     -->             # comment
                                |
                                        <\?.*?\?> | <%.*?%>             # processing instruction
                                |
                                        <[!$]?[-a-zA-Z0-9:_]+   # regular tags
                                        (?>
                                                \s
                                                (?>[^"\'>]+|"[^"]*"|\'[^\']*\')*
                                        )?
                                        >
                                |
                                        <[-a-zA-Z0-9:_]+\s*/> # xml-style empty tag
                                |
                                        </[-a-zA-Z0-9:_]+\s*> # closing tag
                        ').'
                                )
                                }xs';

                while (1) {
                        #
                        # Each loop iteration seach for either the next tag, the next 
                        # openning code span marker, or the next escaped character. 
                        # Each token is then passed to handleSpanToken.
                        #
                        $parts = preg_split($span_re, $str, 2, PREG_SPLIT_DELIM_CAPTURE);
                        
                        # Create token from text preceding tag.
                        if ($parts[0] != "") {
                                $output .= $parts[0];
                        }
                        
                        # Check if we reach the end.
                        if (isset($parts[1])) {
                                $output .= $this->handleSpanToken($parts[1], $parts[2]);
                                $str = $parts[2];
                        }
                        else {
                                break;
                        }
                }
                
                return $output;
        }
        
        
        protected function handleSpanToken($token, &$str) {
        #
        # Handle $token provided by parseSpan by determining its nature and 
        # returning the corresponding value that should replace it.
        #
                switch ($token{0}) {
                        case "\\":
                                return $this->hashPart("&#". ord($token{1}). ";");
                        case "`":
                                # Search for end marker in remaining text.
                                if (preg_match('/^(.*?[^`])'.preg_quote($token).'(?!`)(.*)$/sm', 
                                        $str, $matches))
                                {
                                        $str = $matches[2];
                                        $codespan = $this->makeCodeSpan($matches[1]);
                                        return $this->hashPart($codespan);
                                }
                                return $token; // return as text since no ending marker found.
                        default:
                                return $this->hashPart($token);
                }
        }


        protected function outdent($text) {
        #
        # Remove one level of line-leading tabs or spaces
        #
                return preg_replace('/^(\t|[ ]{1,'.$this->tab_width.'})/m', '', $text);
        }


        # String length function for detab. `_initDetab` will create a function to 
        # hanlde UTF-8 if the default function does not exist.
        protected $utf8_strlen = 'mb_strlen';
        
        protected function detab($text) {
        #
        # Replace tabs with the appropriate amount of space.
        #
                # For each line we separate the line in blocks delemited by
                # tab characters. Then we reconstruct every line by adding the 
                # appropriate number of space between each blocks.
                
                $text = preg_replace_callback('/^.*\t.*$/m',
                        array(&$this, '_detab_callback'), $text);

                return $text;
        }
        protected function _detab_callback($matches) {
                $line = $matches[0];
                $strlen = $this->utf8_strlen; # strlen function for UTF-8.
                
                # Split in blocks.
                $blocks = explode("\t", $line);
                # Add each blocks to the line.
                $line = $blocks[0];
                unset($blocks[0]); # Do not add first block twice.
                foreach ($blocks as $block) {
                        # Calculate amount of space, insert spaces, insert block.
                        $amount = $this->tab_width - 
                                $strlen($line, 'UTF-8') % $this->tab_width;
                        $line .= str_repeat(" ", $amount) . $block;
                }
                return $line;
        }
        protected function _initDetab() {
        #
        # Check for the availability of the function in the `utf8_strlen` property
        # (initially `mb_strlen`). If the function is not available, create a 
        # function that will loosely count the number of UTF-8 characters with a
        # regular expression.
        #
                if (function_exists($this->utf8_strlen)) return;
                $this->utf8_strlen = create_function('$text', 'return preg_match_all(
                        "/[\\\\x00-\\\\xBF]|[\\\\xC0-\\\\xFF][\\\\x80-\\\\xBF]*/", 
                        $text, $m);');
        }


        protected function unhash($text) {
        #
        # Swap back in all the tags hashed by _HashHTMLBlocks.
        #
                return preg_replace_callback('/(.)\x1A[0-9]+\1/', 
                        array(&$this, '_unhash_callback'), $text);
        }
        protected function _unhash_callback($matches) {
                return $this->html_hashes[$matches[0]];
        }

}


#
# Temporary Markdown Extra Parser Implementation Class
#
# NOTE: DON'T USE THIS CLASS
# Currently the implementation of of Extra resides here in this temporary class.
# This makes it easier to propagate the changes between the three different
# packaging styles of PHP Markdown. When this issue is resolved, this
# MarkdownExtra_TmpImpl class here will disappear and \Michelf\MarkdownExtra
# will contain the code. So please use \Michelf\MarkdownExtra and ignore this
# one.
#

abstract class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {

        ### Configuration Variables ###

        # Prefix for footnote ids.
        public $fn_id_prefix = "";
        
        # Optional title attribute for footnote links and backlinks.
        public $fn_link_title = "";
        public $fn_backlink_title = "";
        
        # Optional class attribute for footnote links and backlinks.
        public $fn_link_class = "footnote-ref";
        public $fn_backlink_class = "footnote-backref";

        # Class name for table cell alignment (%% replaced left/center/right)
        # For instance: 'go-%%' becomes 'go-left' or 'go-right' or 'go-center'
        # If empty, the align attribute is used instead of a class name.
        public $table_align_class_tmpl = '';

        # Optional class prefix for fenced code block.
        public $code_class_prefix = "";
        # Class attribute for code blocks goes on the `code` tag;
        # setting this to true will put attributes on the `pre` tag instead.
        public $code_attr_on_pre = false;
        
        # Predefined abbreviations.
        public $predef_abbr = array();


        ### Parser Implementation ###

        public function __construct() {
        #
        # Constructor function. Initialize the parser object.
        #
                # Add extra escapable characters before parent constructor 
                # initialize the table.
                $this->escape_chars .= ':|';
                
                # Insert extra document, block, and span transformations. 
                # Parent constructor will do the sorting.
                $this->document_gamut += array(
                        "doFencedCodeBlocks" => 5,
                        "stripFootnotes"     => 15,
                        "stripAbbreviations" => 25,
                        "appendFootnotes"    => 50,
                        );
                $this->block_gamut += array(
                        "doFencedCodeBlocks" => 5,
                        "doTables"           => 15,
                        "doDefLists"         => 45,
                        );
                $this->span_gamut += array(
                        "doFootnotes"        => 5,
                        "doAbbreviations"    => 70,
                        );
                
                parent::__construct();
        }
        
        
        # Extra variables used during extra transformations.
        protected $footnotes = array();
        protected $footnotes_ordered = array();
        protected $footnotes_ref_count = array();
        protected $footnotes_numbers = array();
        protected $abbr_desciptions = array();
        protected $abbr_word_re = '';
        
        # Give the current footnote number.
        protected $footnote_counter = 1;
        
        
        protected function setup() {
        #
        # Setting up Extra-specific variables.
        #
                parent::setup();
                
                $this->footnotes = array();
                $this->footnotes_ordered = array();
                $this->footnotes_ref_count = array();
                $this->footnotes_numbers = array();
                $this->abbr_desciptions = array();
                $this->abbr_word_re = '';
                $this->footnote_counter = 1;
                
                foreach ($this->predef_abbr as $abbr_word => $abbr_desc) {
                        if ($this->abbr_word_re)
                                $this->abbr_word_re .= '|';
                        $this->abbr_word_re .= preg_quote($abbr_word);
                        $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
                }
        }
        
        protected function teardown() {
        #
        # Clearing Extra-specific variables.
        #
                $this->footnotes = array();
                $this->footnotes_ordered = array();
                $this->footnotes_ref_count = array();
                $this->footnotes_numbers = array();
                $this->abbr_desciptions = array();
                $this->abbr_word_re = '';
                
                parent::teardown();
        }
        
        
        ### Extra Attribute Parser ###

        # Expression to use to catch attributes (includes the braces)
        protected $id_class_attr_catch_re = '\{((?:[ ]*[#.][-_:a-zA-Z0-9]+){1,})[ ]*\}';
        # Expression to use when parsing in a context when no capture is desired
        protected $id_class_attr_nocatch_re = '\{(?:[ ]*[#.][-_:a-zA-Z0-9]+){1,}[ ]*\}';

        protected function doExtraAttributes($tag_name, $attr) {
        #
        # Parse attributes caught by the $this->id_class_attr_catch_re expression
        # and return the HTML-formatted list of attributes.
        #
        # Currently supported attributes are .class and #id.
        #
                if (empty($attr)) return "";
                
                # Split on components
                preg_match_all('/[#.][-_:a-zA-Z0-9]+/', $attr, $matches);
                $elements = $matches[0];

                # handle classes and ids (only first id taken into account)
                $classes = array();
                $id = false;
                foreach ($elements as $element) {
                        if ($element{0} == '.') {
                                $classes[] = substr($element, 1);
                        } else if ($element{0} == '#') {
                                if ($id === false) $id = substr($element, 1);
                        }
                }

                # compose attributes as string
                $attr_str = "";
                if (!empty($id)) {
                        $attr_str .= ' id="'.$id.'"';
                }
                if (!empty($classes)) {
                        $attr_str .= ' class="'.implode(" ", $classes).'"';
                }
                return $attr_str;
        }


        protected function stripLinkDefinitions($text) {
        #
        # Strips link definitions from text, stores the URLs and titles in
        # hash references.
        #
                $less_than_tab = $this->tab_width - 1;

                # Link defs are in the form: ^[id]: url "optional title"
                $text = preg_replace_callback('{
                                                        ^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?: # id = $1
                                                          [ ]*
                                                          \n?                           # maybe *one* newline
                                                          [ ]*
                                                        (?:
                                                          <(.+?)>                       # url = $2
                                                        |
                                                          (\S+?)                        # url = $3
                                                        )
                                                          [ ]*
                                                          \n?                           # maybe one newline
                                                          [ ]*
                                                        (?:
                                                                (?<=\s)                 # lookbehind for whitespace
                                                                ["(]
                                                                (.*?)                   # title = $4
                                                                [")]
                                                                [ ]*
                                                        )?      # title is optional
                                        (?:[ ]* '.$this->id_class_attr_catch_re.' )?  # $5 = extra id & class attr
                                                        (?:\n+|\Z)
                        }xm',
                        array(&$this, '_stripLinkDefinitions_callback'),
                        $text);
                return $text;
        }
        protected function _stripLinkDefinitions_callback($matches) {
                $link_id = strtolower($matches[1]);
                $url = $matches[2] == '' ? $matches[3] : $matches[2];
                $this->urls[$link_id] = $url;
                $this->titles[$link_id] =& $matches[4];
                $this->ref_attr[$link_id] = $this->doExtraAttributes("", $dummy =& $matches[5]);
                return ''; # String that will replace the block
        }


        ### HTML Block Parser ###
        
        # Tags that are always treated as block tags:
        protected $block_tags_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|form|fieldset|iframe|hr|legend|article|section|nav|aside|hgroup|header|footer|figcaption';
                                                   
        # Tags treated as block tags only if the opening tag is alone on its line:
        protected $context_block_tags_re = 'script|noscript|ins|del|iframe|object|source|track|param|math|svg|canvas|audio|video';
        
        # Tags where markdown="1" default to span mode:
        protected $contain_span_tags_re = 'p|h[1-6]|li|dd|dt|td|th|legend|address';
        
        # Tags which must not have their contents modified, no matter where 
        # they appear:
        protected $clean_tags_re = 'script|math|svg';
        
        # Tags that do not need to be closed.
        protected $auto_close_tags_re = 'hr|img|param|source|track';
        

        protected function hashHTMLBlocks($text) {
        #
        # Hashify HTML Blocks and "clean tags".
        #
        # We only want to do this for block-level HTML tags, such as headers,
        # lists, and tables. That's because we still want to wrap <p>s around
        # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        # phrase emphasis, and spans. The list of tags we're looking for is
        # hard-coded.
        #
        # This works by calling _HashHTMLBlocks_InMarkdown, which then calls
        # _HashHTMLBlocks_InHTML when it encounter block tags. When the markdown="1" 
        # attribute is found within a tag, _HashHTMLBlocks_InHTML calls back
        #  _HashHTMLBlocks_InMarkdown to handle the Markdown syntax within the tag.
        # These two functions are calling each other. It's recursive!
        #
                if ($this->no_markup)  return $text;

                #
                # Call the HTML-in-Markdown hasher.
                #
                list($text, ) = $this->_hashHTMLBlocks_inMarkdown($text);
                
                return $text;
        }
        protected function _hashHTMLBlocks_inMarkdown($text, $indent = 0,
                                                                                $enclosing_tag_re = '', $span = false)
        {
        #
        # Parse markdown text, calling _HashHTMLBlocks_InHTML for block tags.
        #
        # *   $indent is the number of space to be ignored when checking for code 
        #     blocks. This is important because if we don't take the indent into 
        #     account, something like this (which looks right) won't work as expected:
        #
        #     <div>
        #         <div markdown="1">
        #         Hello World.  <-- Is this a Markdown code block or text?
        #         </div>  <-- Is this a Markdown code block or a real tag?
        #     <div>
        #
        #     If you don't like this, just don't indent the tag on which
        #     you apply the markdown="1" attribute.
        #
        # *   If $enclosing_tag_re is not empty, stops at the first unmatched closing 
        #     tag with that name. Nested tags supported.
        #
        # *   If $span is true, text inside must treated as span. So any double 
        #     newline will be replaced by a single newline so that it does not create 
        #     paragraphs.
        #
        # Returns an array of that form: ( processed text , remaining text )
        #
                if ($text === '') return array('', '');

                # Regex to check for the presense of newlines around a block tag.
                $newline_before_re = '/(?:^\n?|\n\n)*$/';
                $newline_after_re = 
                        '{
                                ^                                               # Start of text following the tag.
                                (?>[ ]*<!--.*?-->)?             # Optional comment.
                                [ ]*\n                                  # Must be followed by newline.
                        }xs';
                
                # Regex to match any tag.
                $block_tag_re =
                        '{
                                (                                       # $2: Capture whole tag.
                                        </?                                     # Any opening or closing tag.
                                                (?>                             # Tag name.
                                                        '.$this->block_tags_re.'                        |
                                                        '.$this->context_block_tags_re.'        |
                                                        '.$this->clean_tags_re.'                |
                                                        (?!\s)'.$enclosing_tag_re.'
                                                )
                                                (?:
                                                        (?=[\s"\'/a-zA-Z0-9])   # Allowed characters after tag name.
                                                        (?>
                                                                ".*?"           |       # Double quotes (can contain `>`)
                                                                \'.*?\'         |       # Single quotes (can contain `>`)
                                                                .+?                             # Anything but quotes and `>`.
                                                        )*?
                                                )?
                                        >                                       # End of tag.
                                |
                                        <!--    .*?     -->     # HTML Comment
                                |
                                        <\?.*?\?> | <%.*?%>     # Processing instruction
                                |
                                        <!\[CDATA\[.*?\]\]>     # CData Block
                                '. ( !$span ? ' # If not in span.
                                |
                                        # Indented code block
                                        (?: ^[ ]*\n | ^ | \n[ ]*\n )
                                        [ ]{'.($indent+4).'}[^\n]* \n
                                        (?>
                                                (?: [ ]{'.($indent+4).'}[^\n]* | [ ]* ) \n
                                        )*
                                |
                                        # Fenced code block marker
                                        (?<= ^ | \n )
                                        [ ]{0,'.($indent+3).'}(?:~{3,}|`{3,})
                                                                        [ ]*
                                        (?:
                                        \.?[-_:a-zA-Z0-9]+ # standalone class name
                                        |
                                                '.$this->id_class_attr_nocatch_re.' # extra attributes
                                        )?
                                        [ ]*
                                        (?= \n )
                                ' : '' ). ' # End (if not is span).
                                |
                                        # Code span marker
                                        # Note, this regex needs to go after backtick fenced
                                        # code blocks but it should also be kept outside of the
                                        # "if not in span" condition adding backticks to the parser
                                        `+
                                )
                        }xs';

                
                $depth = 0;             # Current depth inside the tag tree.
                $parsed = "";   # Parsed text that will be returned.

                #
                # Loop through every tag until we find the closing tag of the parent
                # or loop until reaching the end of text if no parent tag specified.
                #
                do {
                        #
                        # Split the text using the first $tag_match pattern found.
                        # Text before  pattern will be first in the array, text after
                        # pattern will be at the end, and between will be any catches made 
                        # by the pattern.
                        #
                        $parts = preg_split($block_tag_re, $text, 2, 
                                                                PREG_SPLIT_DELIM_CAPTURE);
                        
                        # If in Markdown span mode, add a empty-string span-level hash 
                        # after each newline to prevent triggering any block element.
                        if ($span) {
                                $void = $this->hashPart("", ':');
                                $newline = "$void\n";
                                $parts[0] = $void . str_replace("\n", $newline, $parts[0]) . $void;
                        }
                        
                        $parsed .= $parts[0]; # Text before current tag.
                        
                        # If end of $text has been reached. Stop loop.
                        if (count($parts) < 3) {
                                $text = "";
                                break;
                        }
                        
                        $tag  = $parts[1]; # Tag to handle.
                        $text = $parts[2]; # Remaining text after current tag.
                        $tag_re = preg_quote($tag); # For use in a regular expression.
                        
                        #
                        # Check for: Fenced code block marker.
                        # Note: need to recheck the whole tag to disambiguate backtick
                        # fences from code spans
                        #
                        if (preg_match('{^\n?([ ]{0,'.($indent+3).'})(~{3,}|`{3,})[ ]*(?:\.?[-_:a-zA-Z0-9]+|'.$this->id_class_attr_nocatch_re.')?[ ]*\n?$}', $tag, $capture)) {
                                # Fenced code block marker: find matching end marker.
                                $fence_indent = strlen($capture[1]); # use captured indent in re
                                $fence_re = $capture[2]; # use captured fence in re
                                if (preg_match('{^(?>.*\n)*?[ ]{'.($fence_indent).'}'.$fence_re.'[ ]*(?:\n|$)}', $text,
                                        $matches)) 
                                {
                                        # End marker found: pass text unchanged until marker.
                                        $parsed .= $tag . $matches[0];
                                        $text = substr($text, strlen($matches[0]));
                                }
                                else {
                                        # No end marker: just skip it.
                                        $parsed .= $tag;
                                }
                        }
                        #
                        # Check for: Indented code block.
                        #
                        else if ($tag{0} == "\n" || $tag{0} == " ") {
                                # Indented code block: pass it unchanged, will be handled 
                                # later.
                                $parsed .= $tag;
                        }
                        #
                        # Check for: Code span marker
                        # Note: need to check this after backtick fenced code blocks
                        #
                        else if ($tag{0} == "`") {
                                # Find corresponding end marker.
                                $tag_re = preg_quote($tag);
                                if (preg_match('{^(?>.+?|\n(?!\n))*?(?<!`)'.$tag_re.'(?!`)}',
                                        $text, $matches))
                                {
                                        # End marker found: pass text unchanged until marker.
                                        $parsed .= $tag . $matches[0];
                                        $text = substr($text, strlen($matches[0]));
                                }
                                else {
                                        # Unmatched marker: just skip it.
                                        $parsed .= $tag;
                                }
                        }
                        #
                        # Check for: Opening Block level tag or
                        #            Opening Context Block tag (like ins and del) 
                        #               used as a block tag (tag is alone on it's line).
                        #
                        else if (preg_match('{^<(?:'.$this->block_tags_re.')\b}', $tag) ||
                                (       preg_match('{^<(?:'.$this->context_block_tags_re.')\b}', $tag) &&
                                        preg_match($newline_before_re, $parsed) &&
                                        preg_match($newline_after_re, $text)    )
                                )
                        {
                                # Need to parse tag and following text using the HTML parser.
                                list($block_text, $text) = 
                                        $this->_hashHTMLBlocks_inHTML($tag . $text, "hashBlock", true);
                                
                                # Make sure it stays outside of any paragraph by adding newlines.
                                $parsed .= "\n\n$block_text\n\n";
                        }
                        #
                        # Check for: Clean tag (like script, math)
                        #            HTML Comments, processing instructions.
                        #
                        else if (preg_match('{^<(?:'.$this->clean_tags_re.')\b}', $tag) ||
                                $tag{1} == '!' || $tag{1} == '?')
                        {
                                # Need to parse tag and following text using the HTML parser.
                                # (don't check for markdown attribute)
                                list($block_text, $text) = 
                                        $this->_hashHTMLBlocks_inHTML($tag . $text, "hashClean", false);
                                
                                $parsed .= $block_text;
                        }
                        #
                        # Check for: Tag with same name as enclosing tag.
                        #
                        else if ($enclosing_tag_re !== '' &&
                                # Same name as enclosing tag.
                                preg_match('{^</?(?:'.$enclosing_tag_re.')\b}', $tag))
                        {
                                #
                                # Increase/decrease nested tag count.
                                #
                                if ($tag{1} == '/')                                             $depth--;
                                else if ($tag{strlen($tag)-2} != '/')   $depth++;

                                if ($depth < 0) {
                                        #
                                        # Going out of parent element. Clean up and break so we
                                        # return to the calling function.
                                        #
                                        $text = $tag . $text;
                                        break;
                                }
                                
                                $parsed .= $tag;
                        }
                        else {
                                $parsed .= $tag;
                        }
                } while ($depth >= 0);
                
                return array($parsed, $text);
        }
        protected function _hashHTMLBlocks_inHTML($text, $hash_method, $md_attr) {
        #
        # Parse HTML, calling _HashHTMLBlocks_InMarkdown for block tags.
        #
        # *   Calls $hash_method to convert any blocks.
        # *   Stops when the first opening tag closes.
        # *   $md_attr indicate if the use of the `markdown="1"` attribute is allowed.
        #     (it is not inside clean tags)
        #
        # Returns an array of that form: ( processed text , remaining text )
        #
                if ($text === '') return array('', '');
                
                # Regex to match `markdown` attribute inside of a tag.
                $markdown_attr_re = '
                        {
                                \s*                     # Eat whitespace before the `markdown` attribute
                                markdown
                                \s*=\s*
                                (?>
                                        (["\'])         # $1: quote delimiter           
                                        (.*?)           # $2: attribute value
                                        \1                      # matching delimiter    
                                |
                                        ([^\s>]*)       # $3: unquoted attribute value
                                )
                                ()                              # $4: make $3 always defined (avoid warnings)
                        }xs';
                
                # Regex to match any tag.
                $tag_re = '{
                                (                                       # $2: Capture whole tag.
                                        </?                                     # Any opening or closing tag.
                                                [\w:$]+                 # Tag name.
                                                (?:
                                                        (?=[\s"\'/a-zA-Z0-9])   # Allowed characters after tag name.
                                                        (?>
                                                                ".*?"           |       # Double quotes (can contain `>`)
                                                                \'.*?\'         |       # Single quotes (can contain `>`)
                                                                .+?                             # Anything but quotes and `>`.
                                                        )*?
                                                )?
                                        >                                       # End of tag.
                                |
                                        <!--    .*?     -->     # HTML Comment
                                |
                                        <\?.*?\?> | <%.*?%>     # Processing instruction
                                |
                                        <!\[CDATA\[.*?\]\]>     # CData Block
                                )
                        }xs';
                
                $original_text = $text;         # Save original text in case of faliure.
                
                $depth          = 0;    # Current depth inside the tag tree.
                $block_text     = "";   # Temporary text holder for current text.
                $parsed         = "";   # Parsed text that will be returned.

                #
                # Get the name of the starting tag.
                # (This pattern makes $base_tag_name_re safe without quoting.)
                #
                if (preg_match('/^<([\w:$]*)\b/', $text, $matches))
                        $base_tag_name_re = $matches[1];

                #
                # Loop through every tag until we find the corresponding closing tag.
                #
                do {
                        #
                        # Split the text using the first $tag_match pattern found.
                        # Text before  pattern will be first in the array, text after
                        # pattern will be at the end, and between will be any catches made 
                        # by the pattern.
                        #
                        $parts = preg_split($tag_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
                        
                        if (count($parts) < 3) {
                                #
                                # End of $text reached with unbalenced tag(s).
                                # In that case, we return original text unchanged and pass the
                                # first character as filtered to prevent an infinite loop in the 
                                # parent function.
                                #
                                return array($original_text{0}, substr($original_text, 1));
                        }
                        
                        $block_text .= $parts[0]; # Text before current tag.
                        $tag         = $parts[1]; # Tag to handle.
                        $text        = $parts[2]; # Remaining text after current tag.
                        
                        #
                        # Check for: Auto-close tag (like <hr/>)
                        #                        Comments and Processing Instructions.
                        #
                        if (preg_match('{^</?(?:'.$this->auto_close_tags_re.')\b}', $tag) ||
                                $tag{1} == '!' || $tag{1} == '?')
                        {
                                # Just add the tag to the block as if it was text.
                                $block_text .= $tag;
                        }
                        else {
                                #
                                # Increase/decrease nested tag count. Only do so if
                                # the tag's name match base tag's.
                                #
                                if (preg_match('{^</?'.$base_tag_name_re.'\b}', $tag)) {
                                        if ($tag{1} == '/')                                             $depth--;
                                        else if ($tag{strlen($tag)-2} != '/')   $depth++;
                                }
                                
                                #
                                # Check for `markdown="1"` attribute and handle it.
                                #
                                if ($md_attr && 
                                        preg_match($markdown_attr_re, $tag, $attr_m) &&
                                        preg_match('/^1|block|span$/', $attr_m[2] . $attr_m[3]))
                                {
                                        # Remove `markdown` attribute from opening tag.
                                        $tag = preg_replace($markdown_attr_re, '', $tag);
                                        
                                        # Check if text inside this tag must be parsed in span mode.
                                        $this->mode = $attr_m[2] . $attr_m[3];
                                        $span_mode = $this->mode == 'span' || $this->mode != 'block' &&
                                                preg_match('{^<(?:'.$this->contain_span_tags_re.')\b}', $tag);
                                        
                                        # Calculate indent before tag.
                                        if (preg_match('/(?:^|\n)( *?)(?! ).*?$/', $block_text, $matches)) {
                                                $strlen = $this->utf8_strlen;
                                                $indent = $strlen($matches[1], 'UTF-8');
                                        } else {
                                                $indent = 0;
                                        }
                                        
                                        # End preceding block with this tag.
                                        $block_text .= $tag;
                                        $parsed .= $this->$hash_method($block_text);
                                        
                                        # Get enclosing tag name for the ParseMarkdown function.
                                        # (This pattern makes $tag_name_re safe without quoting.)
                                        preg_match('/^<([\w:$]*)\b/', $tag, $matches);
                                        $tag_name_re = $matches[1];
                                        
                                        # Parse the content using the HTML-in-Markdown parser.
                                        list ($block_text, $text)
                                                = $this->_hashHTMLBlocks_inMarkdown($text, $indent, 
                                                        $tag_name_re, $span_mode);
                                        
                                        # Outdent markdown text.
                                        if ($indent > 0) {
                                                $block_text = preg_replace("/^[ ]{1,$indent}/m", "", 
                                                                                                        $block_text);
                                        }
                                        
                                        # Append tag content to parsed text.
                                        if (!$span_mode)        $parsed .= "\n\n$block_text\n\n";
                                        else                            $parsed .= "$block_text";
                                        
                                        # Start over with a new block.
                                        $block_text = "";
                                }
                                else $block_text .= $tag;
                        }
                        
                } while ($depth > 0);
                
                #
                # Hash last block text that wasn't processed inside the loop.
                #
                $parsed .= $this->$hash_method($block_text);
                
                return array($parsed, $text);
        }


        protected function hashClean($text) {
        #
        # Called whenever a tag must be hashed when a function inserts a "clean" tag
        # in $text, it passes through this function and is automaticaly escaped, 
        # blocking invalid nested overlap.
        #
                return $this->hashPart($text, 'C');
        }


        protected function doAnchors($text) {
        #
        # Turn Markdown link shortcuts into XHTML <a> tags.
        #
                if ($this->in_anchor) return $text;
                $this->in_anchor = true;
                
                #
                # First, handle reference-style links: [link text] [id]
                #
                $text = preg_replace_callback('{
                        (                                       # wrap whole match in $1
                          \[
                                ('.$this->nested_brackets_re.') # link text = $2
                          \]

                          [ ]?                          # one optional space
                          (?:\n[ ]*)?           # one optional newline followed by spaces

                          \[
                                (.*?)           # id = $3
                          \]
                        )
                        }xs',
                        array(&$this, '_doAnchors_reference_callback'), $text);

                #
                # Next, inline-style links: [link text](url "optional title")
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          \[
                                ('.$this->nested_brackets_re.') # link text = $2
                          \]
                          \(                    # literal paren
                                [ \n]*
                                (?:
                                        <(.+?)> # href = $3
                                |
                                        ('.$this->nested_url_parenthesis_re.')  # href = $4
                                )
                                [ \n]*
                                (                       # $5
                                  ([\'"])       # quote char = $6
                                  (.*?)         # Title = $7
                                  \6            # matching quote
                                  [ \n]*        # ignore any spaces/tabs between closing quote and )
                                )?                      # title is optional
                          \)
                          (?:[ ]? '.$this->id_class_attr_catch_re.' )?   # $8 = id/class attributes
                        )
                        }xs',
                        array(&$this, '_doAnchors_inline_callback'), $text);

                #
                # Last, handle reference-style shortcuts: [link text]
                # These must come last in case you've also got [link text][1]
                # or [link text](/foo)
                #
                $text = preg_replace_callback('{
                        (                                       # wrap whole match in $1
                          \[
                                ([^\[\]]+)              # link text = $2; can\'t contain [ or ]
                          \]
                        )
                        }xs',
                        array(&$this, '_doAnchors_reference_callback'), $text);

                $this->in_anchor = false;
                return $text;
        }
        protected function _doAnchors_reference_callback($matches) {
                $whole_match =  $matches[1];
                $link_text   =  $matches[2];
                $link_id     =& $matches[3];

                if ($link_id == "") {
                        # for shortcut links like [this][] or [this].
                        $link_id = $link_text;
                }
                
                # lower-case and turn embedded newlines into spaces
                $link_id = strtolower($link_id);
                $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

                if (isset($this->urls[$link_id])) {
                        $url = $this->urls[$link_id];
                        $url = $this->encodeAttribute($url);
                        
                        $result = "<a href=\"$url\"";
                        if ( isset( $this->titles[$link_id] ) ) {
                                $title = $this->titles[$link_id];
                                $title = $this->encodeAttribute($title);
                                $result .=  " title=\"$title\"";
                        }
                        if (isset($this->ref_attr[$link_id]))
                                $result .= $this->ref_attr[$link_id];
                
                        $link_text = $this->runSpanGamut($link_text);
                        $result .= ">$link_text</a>";
                        $result = $this->hashPart($result);
                }
                else {
                        $result = $whole_match;
                }
                return $result;
        }
        protected function _doAnchors_inline_callback($matches) {
                $whole_match    =  $matches[1];
                $link_text              =  $this->runSpanGamut($matches[2]);
                $url                    =  $matches[3] == '' ? $matches[4] : $matches[3];
                $title                  =& $matches[7];
                $attr  = $this->doExtraAttributes("a", $dummy =& $matches[8]);


                $url = $this->encodeAttribute($url);

                $result = "<a href=\"$url\"";
                if (isset($title)) {
                        $title = $this->encodeAttribute($title);
                        $result .=  " title=\"$title\"";
                }
                $result .= $attr;
                
                $link_text = $this->runSpanGamut($link_text);
                $result .= ">$link_text</a>";

                return $this->hashPart($result);
        }


        protected function doImages($text) {
        #
        # Turn Markdown image shortcuts into <img> tags.
        #
                #
                # First, handle reference-style labeled images: ![alt text][id]
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          !\[
                                ('.$this->nested_brackets_re.')         # alt text = $2
                          \]

                          [ ]?                          # one optional space
                          (?:\n[ ]*)?           # one optional newline followed by spaces

                          \[
                                (.*?)           # id = $3
                          \]

                        )
                        }xs', 
                        array(&$this, '_doImages_reference_callback'), $text);

                #
                # Next, handle inline images:  ![alt text](url "optional title")
                # Don't forget: encode * and _
                #
                $text = preg_replace_callback('{
                        (                               # wrap whole match in $1
                          !\[
                                ('.$this->nested_brackets_re.')         # alt text = $2
                          \]
                          \s?                   # One optional whitespace character
                          \(                    # literal paren
                                [ \n]*
                                (?:
                                        <(\S*)> # src url = $3
                                |
                                        ('.$this->nested_url_parenthesis_re.')  # src url = $4
                                )
                                [ \n]*
                                (                       # $5
                                  ([\'"])       # quote char = $6
                                  (.*?)         # title = $7
                                  \6            # matching quote
                                  [ \n]*
                                )?                      # title is optional
                          \)
                          (?:[ ]? '.$this->id_class_attr_catch_re.' )?   # $8 = id/class attributes
                        )
                        }xs',
                        array(&$this, '_doImages_inline_callback'), $text);

                return $text;
        }
        protected function _doImages_reference_callback($matches) {
                $whole_match = $matches[1];
                $alt_text    = $matches[2];
                $link_id     = strtolower($matches[3]);

                if ($link_id == "") {
                        $link_id = strtolower($alt_text); # for shortcut links like ![this][].
                }

                $alt_text = $this->encodeAttribute($alt_text);
                if (isset($this->urls[$link_id])) {
                        $url = $this->encodeAttribute($this->urls[$link_id]);
                        $result = "<img src=\"$url\" alt=\"$alt_text\"";
                        if (isset($this->titles[$link_id])) {
                                $title = $this->titles[$link_id];
                                $title = $this->encodeAttribute($title);
                                $result .=  " title=\"$title\"";
                        }
                        if (isset($this->ref_attr[$link_id]))
                                $result .= $this->ref_attr[$link_id];
                        $result .= $this->empty_element_suffix;
                        $result = $this->hashPart($result);
                }
                else {
                        # If there's no such link ID, leave intact:
                        $result = $whole_match;
                }

                return $result;
        }
        protected function _doImages_inline_callback($matches) {
                $whole_match    = $matches[1];
                $alt_text               = $matches[2];
                $url                    = $matches[3] == '' ? $matches[4] : $matches[3];
                $title                  =& $matches[7];
                $attr  = $this->doExtraAttributes("img", $dummy =& $matches[8]);

                $alt_text = $this->encodeAttribute($alt_text);
                $url = $this->encodeAttribute($url);
                $result = "<img src=\"$url\" alt=\"$alt_text\"";
                if (isset($title)) {
                        $title = $this->encodeAttribute($title);
                        $result .=  " title=\"$title\""; # $title already quoted
                }
                $result .= $attr;
                $result .= $this->empty_element_suffix;

                return $this->hashPart($result);
        }


        protected function doHeaders($text) {
        #
        # Redefined to add id and class attribute support.
        #
                # Setext-style headers:
                #         Header 1  {#header1}
                #         ========
                #  
                #         Header 2  {#header2 .class1 .class2}
                #         --------
                #
                $text = preg_replace_callback(
                        '{
                                (^.+?)                                                          # $1: Header text
                                (?:[ ]+ '.$this->id_class_attr_catch_re.' )?     # $3 = id/class attributes
                                [ ]*\n(=+|-+)[ ]*\n+                            # $3: Header footer
                        }mx',
                        array(&$this, '_doHeaders_callback_setext'), $text);

                # atx-style headers:
                #       # Header 1        {#header1}
                #       ## Header 2       {#header2}
                #       ## Header 2 with closing hashes ##  {#header3.class1.class2}
                #       ...
                #       ###### Header 6   {.class2}
                #
                $text = preg_replace_callback('{
                                ^(\#{1,6})      # $1 = string of #\'s
                                [ ]*
                                (.+?)           # $2 = Header text
                                [ ]*
                                \#*                     # optional closing #\'s (not counted)
                                (?:[ ]+ '.$this->id_class_attr_catch_re.' )?     # $3 = id/class attributes
                                [ ]*
                                \n+
                        }xm',
                        array(&$this, '_doHeaders_callback_atx'), $text);

                return $text;
        }
        protected function _doHeaders_callback_setext($matches) {
                if ($matches[3] == '-' && preg_match('{^- }', $matches[1]))
                        return $matches[0];
                $level = $matches[3]{0} == '=' ? 1 : 2;
                $attr  = $this->doExtraAttributes("h$level", $dummy =& $matches[2]);
                $block = "<h$level$attr>".$this->runSpanGamut($matches[1])."</h$level>";
                return "\n" . $this->hashBlock($block) . "\n\n";
        }
        protected function _doHeaders_callback_atx($matches) {
                $level = strlen($matches[1]);
                $attr  = $this->doExtraAttributes("h$level", $dummy =& $matches[3]);
                $block = "<h$level$attr>".$this->runSpanGamut($matches[2])."</h$level>";
                return "\n" . $this->hashBlock($block) . "\n\n";
        }


        protected function doTables($text) {
        #
        # Form HTML tables.
        #
                $less_than_tab = $this->tab_width - 1;
                #
                # Find tables with leading pipe.
                #
                #       | Header 1 | Header 2
                #       | -------- | --------
                #       | Cell 1   | Cell 2
                #       | Cell 3   | Cell 4
                #
                $text = preg_replace_callback('
                        {
                                ^                                                       # Start of a line
                                [ ]{0,'.$less_than_tab.'}       # Allowed whitespace.
                                [|]                                                     # Optional leading pipe (present)
                                (.+) \n                                         # $1: Header row (at least one pipe)
                                
                                [ ]{0,'.$less_than_tab.'}       # Allowed whitespace.
                                [|] ([ ]*[-:]+[-| :]*) \n       # $2: Header underline
                                
                                (                                                       # $3: Cells
                                        (?>
                                                [ ]*                            # Allowed whitespace.
                                                [|] .* \n                       # Row content.
                                        )*
                                )
                                (?=\n|\Z)                                       # Stop at final double newline.
                        }xm',
                        array(&$this, '_doTable_leadingPipe_callback'), $text);
                
                #
                # Find tables without leading pipe.
                #
                #       Header 1 | Header 2
                #       -------- | --------
                #       Cell 1   | Cell 2
                #       Cell 3   | Cell 4
                #
                $text = preg_replace_callback('
                        {
                                ^                                                       # Start of a line
                                [ ]{0,'.$less_than_tab.'}       # Allowed whitespace.
                                (\S.*[|].*) \n                          # $1: Header row (at least one pipe)
                                
                                [ ]{0,'.$less_than_tab.'}       # Allowed whitespace.
                                ([-:]+[ ]*[|][-| :]*) \n        # $2: Header underline
                                
                                (                                                       # $3: Cells
                                        (?>
                                                .* [|] .* \n            # Row content
                                        )*
                                )
                                (?=\n|\Z)                                       # Stop at final double newline.
                        }xm',
                        array(&$this, '_DoTable_callback'), $text);

                return $text;
        }
        protected function _doTable_leadingPipe_callback($matches) {
                $head           = $matches[1];
                $underline      = $matches[2];
                $content        = $matches[3];
                
                # Remove leading pipe for each row.
                $content        = preg_replace('/^ *[|]/m', '', $content);
                
                return $this->_doTable_callback(array($matches[0], $head, $underline, $content));
        }
        protected function _doTable_makeAlignAttr($alignname)
        {
                if (empty($this->table_align_class_tmpl))
                        return " align=\"$alignname\"";

                $classname = str_replace('%%', $alignname, $this->table_align_class_tmpl);
                return " class=\"$classname\"";
        }
        protected function _doTable_callback($matches) {
                $head           = $matches[1];
                $underline      = $matches[2];
                $content        = $matches[3];

                # Remove any tailing pipes for each line.
                $head           = preg_replace('/[|] *$/m', '', $head);
                $underline      = preg_replace('/[|] *$/m', '', $underline);
                $content        = preg_replace('/[|] *$/m', '', $content);
                
                # Reading alignement from header underline.
                $separators     = preg_split('/ *[|] */', $underline);
                foreach ($separators as $n => $s) {
                        if (preg_match('/^ *-+: *$/', $s))
                                $attr[$n] = $this->_doTable_makeAlignAttr('right');
                        else if (preg_match('/^ *:-+: *$/', $s))
                                $attr[$n] = $this->_doTable_makeAlignAttr('center');
                        else if (preg_match('/^ *:-+ *$/', $s))
                                $attr[$n] = $this->_doTable_makeAlignAttr('left');
                        else
                                $attr[$n] = '';
                }
                
                # Parsing span elements, including code spans, character escapes, 
                # and inline HTML tags, so that pipes inside those gets ignored.
                $head           = $this->parseSpan($head);
                $headers        = preg_split('/ *[|] */', $head);
                $col_count      = count($headers);
                $attr       = array_pad($attr, $col_count, '');
                
                # Write column headers.
                $text = "<table>\n";
                $text .= "<thead>\n";
                $text .= "<tr>\n";
                foreach ($headers as $n => $header)
                        $text .= "  <th$attr[$n]>".$this->runSpanGamut(trim($header))."</th>\n";
                $text .= "</tr>\n";
                $text .= "</thead>\n";
                
                # Split content by row.
                $rows = explode("\n", trim($content, "\n"));
                
                $text .= "<tbody>\n";
                foreach ($rows as $row) {
                        # Parsing span elements, including code spans, character escapes, 
                        # and inline HTML tags, so that pipes inside those gets ignored.
                        $row = $this->parseSpan($row);
                        
                        # Split row by cell.
                        $row_cells = preg_split('/ *[|] */', $row, $col_count);
                        $row_cells = array_pad($row_cells, $col_count, '');
                        
                        $text .= "<tr>\n";
                        foreach ($row_cells as $n => $cell)
                                $text .= "  <td$attr[$n]>".$this->runSpanGamut(trim($cell))."</td>\n";
                        $text .= "</tr>\n";
                }
                $text .= "</tbody>\n";
                $text .= "</table>";
                
                return $this->hashBlock($text) . "\n";
        }

        
        protected function doDefLists($text) {
        #
        # Form HTML definition lists.
        #
                $less_than_tab = $this->tab_width - 1;

                # Re-usable pattern to match any entire dl list:
                $whole_list_re = '(?>
                        (                                                               # $1 = whole list
                          (                                                             # $2
                                [ ]{0,'.$less_than_tab.'}
                                ((?>.*\S.*\n)+)                         # $3 = defined term
                                \n?
                                [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
                          )
                          (?s:.+?)
                          (                                                             # $4
                                  \z
                                |
                                  \n{2,}
                                  (?=\S)
                                  (?!                                           # Negative lookahead for another term
                                        [ ]{0,'.$less_than_tab.'}
                                        (?: \S.*\n )+?                  # defined term
                                        \n?
                                        [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
                                  )
                                  (?!                                           # Negative lookahead for another definition
                                        [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
                                  )
                          )
                        )
                )'; // mx

                $text = preg_replace_callback('{
                                (?>\A\n?|(?<=\n\n))
                                '.$whole_list_re.'
                        }mx',
                        array(&$this, '_doDefLists_callback'), $text);

                return $text;
        }
        protected function _doDefLists_callback($matches) {
                # Re-usable patterns to match list item bullets and number markers:
                $list = $matches[1];
                
                # Turn double returns into triple returns, so that we can make a
                # paragraph for the last item in a list, if necessary:
                $result = trim($this->processDefListItems($list));
                $result = "<dl>\n" . $result . "\n</dl>";
                return $this->hashBlock($result) . "\n\n";
        }


        protected function processDefListItems($list_str) {
        #
        #       Process the contents of a single definition list, splitting it
        #       into individual term and definition list items.
        #
                $less_than_tab = $this->tab_width - 1;
                
                # trim trailing blank lines:
                $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

                # Process definition terms.
                $list_str = preg_replace_callback('{
                        (?>\A\n?|\n\n+)                                 # leading line
                        (                                                               # definition terms = $1
                                [ ]{0,'.$less_than_tab.'}       # leading whitespace
                                (?!\:[ ]|[ ])                           # negative lookahead for a definition
                                                                                        #   mark (colon) or more whitespace.
                                (?> \S.* \n)+?                          # actual term (not whitespace). 
                        )                       
                        (?=\n?[ ]{0,3}:[ ])                             # lookahead for following line feed 
                                                                                        #   with a definition mark.
                        }xm',
                        array(&$this, '_processDefListItems_callback_dt'), $list_str);

                # Process actual definitions.
                $list_str = preg_replace_callback('{
                        \n(\n+)?                                                # leading line = $1
                        (                                                               # marker space = $2
                                [ ]{0,'.$less_than_tab.'}       # whitespace before colon
                                \:[ ]+                                          # definition mark (colon)
                        )
                        ((?s:.+?))                                              # definition text = $3
                        (?= \n+                                                 # stop at next definition mark,
                                (?:                                                     # next term or end of text
                                        [ ]{0,'.$less_than_tab.'} \:[ ] |
                                        <dt> | \z
                                )                                               
                        )                                       
                        }xm',
                        array(&$this, '_processDefListItems_callback_dd'), $list_str);

                return $list_str;
        }
        protected function _processDefListItems_callback_dt($matches) {
                $terms = explode("\n", trim($matches[1]));
                $text = '';
                foreach ($terms as $term) {
                        $term = $this->runSpanGamut(trim($term));
                        $text .= "\n<dt>" . $term . "</dt>";
                }
                return $text . "\n";
        }
        protected function _processDefListItems_callback_dd($matches) {
                $leading_line   = $matches[1];
                $marker_space   = $matches[2];
                $def                    = $matches[3];

                if ($leading_line || preg_match('/\n{2,}/', $def)) {
                        # Replace marker with the appropriate whitespace indentation
                        $def = str_repeat(' ', strlen($marker_space)) . $def;
                        $def = $this->runBlockGamut($this->outdent($def . "\n\n"));
                        $def = "\n". $def ."\n";
                }
                else {
                        $def = rtrim($def);
                        $def = $this->runSpanGamut($this->outdent($def));
                }

                return "\n<dd>" . $def . "</dd>\n";
        }


        protected function doFencedCodeBlocks($text) {
        #
        # Adding the fenced code block syntax to regular Markdown:
        #
        # ~~~
        # Code block
        # ~~~
        #
                $less_than_tab = $this->tab_width;
                
                $text = preg_replace_callback('{
                                (?:\n|\A)
                                # 1: Opening marker
                                (
                                        (?:~{3,}|`{3,}) # 3 or more tildes/backticks.
                                )
                                [ ]*
                                (?:
                                        \.?([-_:a-zA-Z0-9]+) # 2: standalone class name
                                |
                                        '.$this->id_class_attr_catch_re.' # 3: Extra attributes
                                )?
                                [ ]* \n # Whitespace and newline following marker.
                                
                                # 4: Content
                                (
                                        (?>
                                                (?!\1 [ ]* \n)  # Not a closing marker.
                                                .*\n+
                                        )+
                                )
                                
                                # Closing marker.
                                \1 [ ]* (?= \n )
                        }xm',
                        array(&$this, '_doFencedCodeBlocks_callback'), $text);

                return $text;
        }
        protected function _doFencedCodeBlocks_callback($matches) {
                $classname =& $matches[2];
                $attrs     =& $matches[3];
                $codeblock = $matches[4];
                $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);
                $codeblock = preg_replace_callback('/^\n+/',
                        array(&$this, '_doFencedCodeBlocks_newlines'), $codeblock);

                if ($classname != "") {
                        if ($classname{0} == '.')
                                $classname = substr($classname, 1);
                        $attr_str = ' class="'.$this->code_class_prefix.$classname.'"';
                } else {
                        $attr_str = $this->doExtraAttributes($this->code_attr_on_pre ? "pre" : "code", $attrs);
                }
                $pre_attr_str  = $this->code_attr_on_pre ? $attr_str : '';
                $code_attr_str = $this->code_attr_on_pre ? '' : $attr_str;
                $codeblock  = "<pre$pre_attr_str><code$code_attr_str>$codeblock</code></pre>";
                
                return "\n\n".$this->hashBlock($codeblock)."\n\n";
        }
        protected function _doFencedCodeBlocks_newlines($matches) {
                return str_repeat("<br$this->empty_element_suffix", 
                        strlen($matches[0]));
        }


        #
        # Redefining emphasis markers so that emphasis by underscore does not
        # work in the middle of a word.
        #
        protected $em_relist = array(
                ''  => '(?:(?<!\*)\*(?!\*)|(?<![a-zA-Z0-9_])_(?!_))(?=\S|$)(?![\.,:;]\s)',
                '*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
                '_' => '(?<=\S|^)(?<!_)_(?![a-zA-Z0-9_])',
                );
        protected $strong_relist = array(
                ''   => '(?:(?<!\*)\*\*(?!\*)|(?<![a-zA-Z0-9_])__(?!_))(?=\S|$)(?![\.,:;]\s)',
                '**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
                '__' => '(?<=\S|^)(?<!_)__(?![a-zA-Z0-9_])',
                );
        protected $em_strong_relist = array(
                ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<![a-zA-Z0-9_])___(?!_))(?=\S|$)(?![\.,:;]\s)',
                '***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
                '___' => '(?<=\S|^)(?<!_)___(?![a-zA-Z0-9_])',
                );


        protected function formParagraphs($text) {
        #
        #       Params:
        #               $text - string to process with html <p> tags
        #
                # Strip leading and trailing lines:
                $text = preg_replace('/\A\n+|\n+\z/', '', $text);
                
                $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

                #
                # Wrap <p> tags and unhashify HTML blocks
                #
                foreach ($grafs as $key => $value) {
                        $value = trim($this->runSpanGamut($value));
                        
                        # Check if this should be enclosed in a paragraph.
                        # Clean tag hashes & block tag hashes are left alone.
                        $is_p = !preg_match('/^B\x1A[0-9]+B|^C\x1A[0-9]+C$/', $value);
                        
                        if ($is_p) {
                                $value = "<p>$value</p>";
                        }
                        $grafs[$key] = $value;
                }
                
                # Join grafs in one text, then unhash HTML tags. 
                $text = implode("\n\n", $grafs);
                
                # Finish by removing any tag hashes still present in $text.
                $text = $this->unhash($text);
                
                return $text;
        }
        
        
        ### Footnotes
        
        protected function stripFootnotes($text) {
        #
        # Strips link definitions from text, stores the URLs and titles in
        # hash references.
        #
                $less_than_tab = $this->tab_width - 1;

                # Link defs are in the form: [^id]: url "optional title"
                $text = preg_replace_callback('{
                        ^[ ]{0,'.$less_than_tab.'}\[\^(.+?)\][ ]?:      # note_id = $1
                          [ ]*
                          \n?                                   # maybe *one* newline
                        (                                               # text = $2 (no blank lines allowed)
                                (?:                                     
                                        .+                              # actual text
                                |
                                        \n                              # newlines but 
                                        (?!\[\^.+?\]:\s)# negative lookahead for footnote marker.
                                        (?!\n+[ ]{0,3}\S)# ensure line is not blank and followed 
                                                                        # by non-indented content
                                )*
                        )               
                        }xm',
                        array(&$this, '_stripFootnotes_callback'),
                        $text);
                return $text;
        }
        protected function _stripFootnotes_callback($matches) {
                $note_id = $this->fn_id_prefix . $matches[1];
                $this->footnotes[$note_id] = $this->outdent($matches[2]);
                return ''; # String that will replace the block
        }


        protected function doFootnotes($text) {
        #
        # Replace footnote references in $text [^id] with a special text-token 
        # which will be replaced by the actual footnote marker in appendFootnotes.
        #
                if (!$this->in_anchor) {
                        $text = preg_replace('{\[\^(.+?)\]}', "F\x1Afn:\\1\x1A:", $text);
                }
                return $text;
        }

        
        protected function appendFootnotes($text) {
        #
        # Append footnote list to text.
        #
                $text = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}', 
                        array(&$this, '_appendFootnotes_callback'), $text);
        
                if (!empty($this->footnotes_ordered)) {
                        $text .= "\n\n";
                        $text .= "<div class=\"footnotes\">\n";
                        $text .= "<hr". $this->empty_element_suffix ."\n";
                        $text .= "<ol>\n\n";

                        $attr = "";
                        if ($this->fn_backlink_class != "") {
                                $class = $this->fn_backlink_class;
                                $class = $this->encodeAttribute($class);
                                $attr .= " class=\"$class\"";
                        }
                        if ($this->fn_backlink_title != "") {
                                $title = $this->fn_backlink_title;
                                $title = $this->encodeAttribute($title);
                                $attr .= " title=\"$title\"";
                        }
                        $num = 0;
                        
                        while (!empty($this->footnotes_ordered)) {
                                $footnote = reset($this->footnotes_ordered);
                                $note_id = key($this->footnotes_ordered);
                                unset($this->footnotes_ordered[$note_id]);
                                $ref_count = $this->footnotes_ref_count[$note_id];
                                unset($this->footnotes_ref_count[$note_id]);
                                unset($this->footnotes[$note_id]);
                                
                                $footnote .= "\n"; # Need to append newline before parsing.
                                $footnote = $this->runBlockGamut("$footnote\n");                                
                                $footnote = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}', 
                                        array(&$this, '_appendFootnotes_callback'), $footnote);
                                
                                $attr = str_replace("%%", ++$num, $attr);
                                $note_id = $this->encodeAttribute($note_id);

                                # Prepare backlink, multiple backlinks if multiple references
                                $backlink = "<a href=\"#fnref:$note_id\"$attr>&#8617;</a>";
                                for ($ref_num = 2; $ref_num <= $ref_count; ++$ref_num) {
                                        $backlink .= " <a href=\"#fnref$ref_num:$note_id\"$attr>&#8617;</a>";
                                }
                                # Add backlink to last paragraph; create new paragraph if needed.
                                if (preg_match('{</p>$}', $footnote)) {
                                        $footnote = substr($footnote, 0, -4) . "&#160;$backlink</p>";
                                } else {
                                        $footnote .= "\n\n<p>$backlink</p>";
                                }
                                
                                $text .= "<li id=\"fn:$note_id\">\n";
                                $text .= $footnote . "\n";
                                $text .= "</li>\n\n";
                        }
                        
                        $text .= "</ol>\n";
                        $text .= "</div>";
                }
                return $text;
        }
        protected function _appendFootnotes_callback($matches) {
                $node_id = $this->fn_id_prefix . $matches[1];
                
                # Create footnote marker only if it has a corresponding footnote *and*
                # the footnote hasn't been used by another marker.
                if (isset($this->footnotes[$node_id])) {
                        $num =& $this->footnotes_numbers[$node_id];
                        if (!isset($num)) {
                                # Transfer footnote content to the ordered list and give it its
                                # number
                                $this->footnotes_ordered[$node_id] = $this->footnotes[$node_id];
                                $this->footnotes_ref_count[$node_id] = 1;
                                $num = $this->footnote_counter++;
                                $ref_count_mark = '';
                        } else {
                                $ref_count_mark = $this->footnotes_ref_count[$node_id] += 1;
                        }

                        $attr = "";
                        if ($this->fn_link_class != "") {
                                $class = $this->fn_link_class;
                                $class = $this->encodeAttribute($class);
                                $attr .= " class=\"$class\"";
                        }
                        if ($this->fn_link_title != "") {
                                $title = $this->fn_link_title;
                                $title = $this->encodeAttribute($title);
                                $attr .= " title=\"$title\"";
                        }
                        
                        $attr = str_replace("%%", $num, $attr);
                        $node_id = $this->encodeAttribute($node_id);
                        
                        return
                                "<sup id=\"fnref$ref_count_mark:$node_id\">".
                                "<a href=\"#fn:$node_id\"$attr>$num</a>".
                                "</sup>";
                }
                
                return "[^".$matches[1]."]";
        }
                
        
        ### Abbreviations ###
        
        protected function stripAbbreviations($text) {
        #
        # Strips abbreviations from text, stores titles in hash references.
        #
                $less_than_tab = $this->tab_width - 1;

                # Link defs are in the form: [id]*: url "optional title"
                $text = preg_replace_callback('{
                        ^[ ]{0,'.$less_than_tab.'}\*\[(.+?)\][ ]?:      # abbr_id = $1
                        (.*)                                    # text = $2 (no blank lines allowed)    
                        }xm',
                        array(&$this, '_stripAbbreviations_callback'),
                        $text);
                return $text;
        }
        protected function _stripAbbreviations_callback($matches) {
                $abbr_word = $matches[1];
                $abbr_desc = $matches[2];
                if ($this->abbr_word_re)
                        $this->abbr_word_re .= '|';
                $this->abbr_word_re .= preg_quote($abbr_word);
                $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
                return ''; # String that will replace the block
        }
        
        
        protected function doAbbreviations($text) {
        #
        # Find defined abbreviations in text and wrap them in <abbr> elements.
        #
                if ($this->abbr_word_re) {
                        // cannot use the /x modifier because abbr_word_re may 
                        // contain significant spaces:
                        $text = preg_replace_callback('{'.
                                '(?<![\w\x1A])'.
                                '(?:'.$this->abbr_word_re.')'.
                                '(?![\w\x1A])'.
                                '}', 
                                array(&$this, '_doAbbreviations_callback'), $text);
                }
                return $text;
        }
        protected function _doAbbreviations_callback($matches) {
                $abbr = $matches[0];
                if (isset($this->abbr_desciptions[$abbr])) {
                        $desc = $this->abbr_desciptions[$abbr];
                        if (empty($desc)) {
                                return $this->hashPart("<abbr>$abbr</abbr>");
                        } else {
                                $desc = $this->encodeAttribute($desc);
                                return $this->hashPart("<abbr title=\"$desc\">$abbr</abbr>");
                        }
                } else {
                        return $matches[0];
                }
        }

}