2 :mod:`xml.parsers.expat` --- Fast XML parsing using Expat
3 =========================================================
5 .. module:: xml.parsers.expat
6 :synopsis: An interface to the Expat non-validating XML parser.
7 .. moduleauthor:: Paul Prescod <paul@prescod.net>
12 Many of the attributes of the XMLParser objects are callbacks. Since
13 signature information must be presented, these are described using the method
14 directive. Since they are attributes which are set by client code, in-text
15 references to these attributes should be marked using the :member: role.
19 .. index:: single: Expat
21 The :mod:`xml.parsers.expat` module is a Python interface to the Expat
22 non-validating XML parser. The module provides a single extension type,
23 :class:`xmlparser`, that represents the current state of an XML parser. After
24 an :class:`xmlparser` object has been created, various attributes of the object
25 can be set to handler functions. When an XML document is then fed to the
26 parser, the handler functions are called for the character data and markup in
29 .. index:: module: pyexpat
31 This module uses the :mod:`pyexpat` module to provide access to the Expat
32 parser. Direct use of the :mod:`pyexpat` module is deprecated.
34 This module provides one exception and one type object:
37 .. exception:: ExpatError
39 The exception raised when Expat reports an error. See section
40 :ref:`expaterror-objects` for more information on interpreting Expat errors.
45 Alias for :exc:`ExpatError`.
48 .. data:: XMLParserType
50 The type of the return values from the :func:`ParserCreate` function.
52 The :mod:`xml.parsers.expat` module contains two functions:
55 .. function:: ErrorString(errno)
57 Returns an explanatory string for a given error number *errno*.
60 .. function:: ParserCreate([encoding[, namespace_separator]])
62 Creates and returns a new :class:`xmlparser` object. *encoding*, if specified,
63 must be a string naming the encoding used by the XML data. Expat doesn't
64 support as many encodings as Python does, and its repertoire of encodings can't
65 be extended; it supports UTF-8, UTF-16, ISO-8859-1 (Latin1), and ASCII. If
66 *encoding* [1]_ is given it will override the implicit or explicit encoding of the
69 Expat can optionally do XML namespace processing for you, enabled by providing a
70 value for *namespace_separator*. The value must be a one-character string; a
71 :exc:`ValueError` will be raised if the string has an illegal length (``None``
72 is considered the same as omission). When namespace processing is enabled,
73 element type names and attribute names that belong to a namespace will be
74 expanded. The element name passed to the element handlers
75 :attr:`StartElementHandler` and :attr:`EndElementHandler` will be the
76 concatenation of the namespace URI, the namespace separator character, and the
77 local part of the name. If the namespace separator is a zero byte (``chr(0)``)
78 then the namespace URI and the local part will be concatenated without any
81 For example, if *namespace_separator* is set to a space character (``' '``) and
82 the following document is parsed::
85 <root xmlns = "http://default-namespace.org/"
86 xmlns:py = "http://www.python.org/ns/">
91 :attr:`StartElementHandler` will receive the following strings for each
94 http://default-namespace.org/ root
95 http://www.python.org/ns/ elem1
101 `The Expat XML Parser <http://www.libexpat.org/>`_
102 Home page of the Expat project.
105 .. _xmlparser-objects:
110 :class:`xmlparser` objects have the following methods:
113 .. method:: xmlparser.Parse(data[, isfinal])
115 Parses the contents of the string *data*, calling the appropriate handler
116 functions to process the parsed data. *isfinal* must be true on the final call
117 to this method. *data* can be the empty string at any time.
120 .. method:: xmlparser.ParseFile(file)
122 Parse XML data reading from the object *file*. *file* only needs to provide
123 the ``read(nbytes)`` method, returning the empty string when there's no more
127 .. method:: xmlparser.SetBase(base)
129 Sets the base to be used for resolving relative URIs in system identifiers in
130 declarations. Resolving relative identifiers is left to the application: this
131 value will be passed through as the *base* argument to the
132 :func:`ExternalEntityRefHandler`, :func:`NotationDeclHandler`, and
133 :func:`UnparsedEntityDeclHandler` functions.
136 .. method:: xmlparser.GetBase()
138 Returns a string containing the base set by a previous call to :meth:`SetBase`,
139 or ``None`` if :meth:`SetBase` hasn't been called.
142 .. method:: xmlparser.GetInputContext()
144 Returns the input data that generated the current event as a string. The data is
145 in the encoding of the entity which contains the text. When called while an
146 event handler is not active, the return value is ``None``.
148 .. versionadded:: 2.1
151 .. method:: xmlparser.ExternalEntityParserCreate(context[, encoding])
153 Create a "child" parser which can be used to parse an external parsed entity
154 referred to by content parsed by the parent parser. The *context* parameter
155 should be the string passed to the :meth:`ExternalEntityRefHandler` handler
156 function, described below. The child parser is created with the
157 :attr:`ordered_attributes`, :attr:`returns_unicode` and
158 :attr:`specified_attributes` set to the values of this parser.
161 .. method:: xmlparser.UseForeignDTD([flag])
163 Calling this with a true value for *flag* (the default) will cause Expat to call
164 the :attr:`ExternalEntityRefHandler` with :const:`None` for all arguments to
165 allow an alternate DTD to be loaded. If the document does not contain a
166 document type declaration, the :attr:`ExternalEntityRefHandler` will still be
167 called, but the :attr:`StartDoctypeDeclHandler` and
168 :attr:`EndDoctypeDeclHandler` will not be called.
170 Passing a false value for *flag* will cancel a previous call that passed a true
171 value, but otherwise has no effect.
173 This method can only be called before the :meth:`Parse` or :meth:`ParseFile`
174 methods are called; calling it after either of those have been called causes
175 :exc:`ExpatError` to be raised with the :attr:`code` attribute set to
176 :const:`errors.XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING`.
178 .. versionadded:: 2.3
180 :class:`xmlparser` objects have the following attributes:
183 .. attribute:: xmlparser.buffer_size
185 The size of the buffer used when :attr:`buffer_text` is true.
186 A new buffer size can be set by assigning a new integer value
188 When the size is changed, the buffer will be flushed.
190 .. versionadded:: 2.3
192 .. versionchanged:: 2.6
193 The buffer size can now be changed.
195 .. attribute:: xmlparser.buffer_text
197 Setting this to true causes the :class:`xmlparser` object to buffer textual
198 content returned by Expat to avoid multiple calls to the
199 :meth:`CharacterDataHandler` callback whenever possible. This can improve
200 performance substantially since Expat normally breaks character data into chunks
201 at every line ending. This attribute is false by default, and may be changed at
204 .. versionadded:: 2.3
207 .. attribute:: xmlparser.buffer_used
209 If :attr:`buffer_text` is enabled, the number of bytes stored in the buffer.
210 These bytes represent UTF-8 encoded text. This attribute has no meaningful
211 interpretation when :attr:`buffer_text` is false.
213 .. versionadded:: 2.3
216 .. attribute:: xmlparser.ordered_attributes
218 Setting this attribute to a non-zero integer causes the attributes to be
219 reported as a list rather than a dictionary. The attributes are presented in
220 the order found in the document text. For each attribute, two list entries are
221 presented: the attribute name and the attribute value. (Older versions of this
222 module also used this format.) By default, this attribute is false; it may be
225 .. versionadded:: 2.1
228 .. attribute:: xmlparser.returns_unicode
230 If this attribute is set to a non-zero integer, the handler functions will be
231 passed Unicode strings. If :attr:`returns_unicode` is :const:`False`, 8-bit
232 strings containing UTF-8 encoded data will be passed to the handlers. This is
233 :const:`True` by default when Python is built with Unicode support.
235 .. versionchanged:: 1.6
236 Can be changed at any time to affect the result type.
239 .. attribute:: xmlparser.specified_attributes
241 If set to a non-zero integer, the parser will report only those attributes which
242 were specified in the document instance and not those which were derived from
243 attribute declarations. Applications which set this need to be especially
244 careful to use what additional information is available from the declarations as
245 needed to comply with the standards for the behavior of XML processors. By
246 default, this attribute is false; it may be changed at any time.
248 .. versionadded:: 2.1
250 The following attributes contain values relating to the most recent error
251 encountered by an :class:`xmlparser` object, and will only have correct values
252 once a call to :meth:`Parse` or :meth:`ParseFile` has raised a
253 :exc:`xml.parsers.expat.ExpatError` exception.
256 .. attribute:: xmlparser.ErrorByteIndex
258 Byte index at which an error occurred.
261 .. attribute:: xmlparser.ErrorCode
263 Numeric code specifying the problem. This value can be passed to the
264 :func:`ErrorString` function, or compared to one of the constants defined in the
268 .. attribute:: xmlparser.ErrorColumnNumber
270 Column number at which an error occurred.
273 .. attribute:: xmlparser.ErrorLineNumber
275 Line number at which an error occurred.
277 The following attributes contain values relating to the current parse location
278 in an :class:`xmlparser` object. During a callback reporting a parse event they
279 indicate the location of the first of the sequence of characters that generated
280 the event. When called outside of a callback, the position indicated will be
281 just past the last parse event (regardless of whether there was an associated
284 .. versionadded:: 2.4
287 .. attribute:: xmlparser.CurrentByteIndex
289 Current byte index in the parser input.
292 .. attribute:: xmlparser.CurrentColumnNumber
294 Current column number in the parser input.
297 .. attribute:: xmlparser.CurrentLineNumber
299 Current line number in the parser input.
301 Here is the list of handlers that can be set. To set a handler on an
302 :class:`xmlparser` object *o*, use ``o.handlername = func``. *handlername* must
303 be taken from the following list, and *func* must be a callable object accepting
304 the correct number of arguments. The arguments are all strings, unless
308 .. method:: xmlparser.XmlDeclHandler(version, encoding, standalone)
310 Called when the XML declaration is parsed. The XML declaration is the
311 (optional) declaration of the applicable version of the XML recommendation, the
312 encoding of the document text, and an optional "standalone" declaration.
313 *version* and *encoding* will be strings of the type dictated by the
314 :attr:`returns_unicode` attribute, and *standalone* will be ``1`` if the
315 document is declared standalone, ``0`` if it is declared not to be standalone,
316 or ``-1`` if the standalone clause was omitted. This is only available with
317 Expat version 1.95.0 or newer.
319 .. versionadded:: 2.1
322 .. method:: xmlparser.StartDoctypeDeclHandler(doctypeName, systemId, publicId, has_internal_subset)
324 Called when Expat begins parsing the document type declaration (``<!DOCTYPE
325 ...``). The *doctypeName* is provided exactly as presented. The *systemId* and
326 *publicId* parameters give the system and public identifiers if specified, or
327 ``None`` if omitted. *has_internal_subset* will be true if the document
328 contains and internal document declaration subset. This requires Expat version
332 .. method:: xmlparser.EndDoctypeDeclHandler()
334 Called when Expat is done parsing the document type declaration. This requires
335 Expat version 1.2 or newer.
338 .. method:: xmlparser.ElementDeclHandler(name, model)
340 Called once for each element type declaration. *name* is the name of the
341 element type, and *model* is a representation of the content model.
344 .. method:: xmlparser.AttlistDeclHandler(elname, attname, type, default, required)
346 Called for each declared attribute for an element type. If an attribute list
347 declaration declares three attributes, this handler is called three times, once
348 for each attribute. *elname* is the name of the element to which the
349 declaration applies and *attname* is the name of the attribute declared. The
350 attribute type is a string passed as *type*; the possible values are
351 ``'CDATA'``, ``'ID'``, ``'IDREF'``, ... *default* gives the default value for
352 the attribute used when the attribute is not specified by the document instance,
353 or ``None`` if there is no default value (``#IMPLIED`` values). If the
354 attribute is required to be given in the document instance, *required* will be
355 true. This requires Expat version 1.95.0 or newer.
358 .. method:: xmlparser.StartElementHandler(name, attributes)
360 Called for the start of every element. *name* is a string containing the
361 element name, and *attributes* is a dictionary mapping attribute names to their
365 .. method:: xmlparser.EndElementHandler(name)
367 Called for the end of every element.
370 .. method:: xmlparser.ProcessingInstructionHandler(target, data)
372 Called for every processing instruction.
375 .. method:: xmlparser.CharacterDataHandler(data)
377 Called for character data. This will be called for normal character data, CDATA
378 marked content, and ignorable whitespace. Applications which must distinguish
379 these cases can use the :attr:`StartCdataSectionHandler`,
380 :attr:`EndCdataSectionHandler`, and :attr:`ElementDeclHandler` callbacks to
381 collect the required information.
384 .. method:: xmlparser.UnparsedEntityDeclHandler(entityName, base, systemId, publicId, notationName)
386 Called for unparsed (NDATA) entity declarations. This is only present for
387 version 1.2 of the Expat library; for more recent versions, use
388 :attr:`EntityDeclHandler` instead. (The underlying function in the Expat
389 library has been declared obsolete.)
392 .. method:: xmlparser.EntityDeclHandler(entityName, is_parameter_entity, value, base, systemId, publicId, notationName)
394 Called for all entity declarations. For parameter and internal entities,
395 *value* will be a string giving the declared contents of the entity; this will
396 be ``None`` for external entities. The *notationName* parameter will be
397 ``None`` for parsed entities, and the name of the notation for unparsed
398 entities. *is_parameter_entity* will be true if the entity is a parameter entity
399 or false for general entities (most applications only need to be concerned with
400 general entities). This is only available starting with version 1.95.0 of the
403 .. versionadded:: 2.1
406 .. method:: xmlparser.NotationDeclHandler(notationName, base, systemId, publicId)
408 Called for notation declarations. *notationName*, *base*, and *systemId*, and
409 *publicId* are strings if given. If the public identifier is omitted,
410 *publicId* will be ``None``.
413 .. method:: xmlparser.StartNamespaceDeclHandler(prefix, uri)
415 Called when an element contains a namespace declaration. Namespace declarations
416 are processed before the :attr:`StartElementHandler` is called for the element
417 on which declarations are placed.
420 .. method:: xmlparser.EndNamespaceDeclHandler(prefix)
422 Called when the closing tag is reached for an element that contained a
423 namespace declaration. This is called once for each namespace declaration on
424 the element in the reverse of the order for which the
425 :attr:`StartNamespaceDeclHandler` was called to indicate the start of each
426 namespace declaration's scope. Calls to this handler are made after the
427 corresponding :attr:`EndElementHandler` for the end of the element.
430 .. method:: xmlparser.CommentHandler(data)
432 Called for comments. *data* is the text of the comment, excluding the leading
433 '``<!-``\ ``-``' and trailing '``-``\ ``->``'.
436 .. method:: xmlparser.StartCdataSectionHandler()
438 Called at the start of a CDATA section. This and :attr:`EndCdataSectionHandler`
439 are needed to be able to identify the syntactical start and end for CDATA
443 .. method:: xmlparser.EndCdataSectionHandler()
445 Called at the end of a CDATA section.
448 .. method:: xmlparser.DefaultHandler(data)
450 Called for any characters in the XML document for which no applicable handler
451 has been specified. This means characters that are part of a construct which
452 could be reported, but for which no handler has been supplied.
455 .. method:: xmlparser.DefaultHandlerExpand(data)
457 This is the same as the :func:`DefaultHandler`, but doesn't inhibit expansion
458 of internal entities. The entity reference will not be passed to the default
462 .. method:: xmlparser.NotStandaloneHandler()
464 Called if the XML document hasn't been declared as being a standalone document.
465 This happens when there is an external subset or a reference to a parameter
466 entity, but the XML declaration does not set standalone to ``yes`` in an XML
467 declaration. If this handler returns ``0``, then the parser will throw an
468 :const:`XML_ERROR_NOT_STANDALONE` error. If this handler is not set, no
469 exception is raised by the parser for this condition.
472 .. method:: xmlparser.ExternalEntityRefHandler(context, base, systemId, publicId)
474 Called for references to external entities. *base* is the current base, as set
475 by a previous call to :meth:`SetBase`. The public and system identifiers,
476 *systemId* and *publicId*, are strings if given; if the public identifier is not
477 given, *publicId* will be ``None``. The *context* value is opaque and should
478 only be used as described below.
480 For external entities to be parsed, this handler must be implemented. It is
481 responsible for creating the sub-parser using
482 ``ExternalEntityParserCreate(context)``, initializing it with the appropriate
483 callbacks, and parsing the entity. This handler should return an integer; if it
484 returns ``0``, the parser will throw an
485 :const:`XML_ERROR_EXTERNAL_ENTITY_HANDLING` error, otherwise parsing will
488 If this handler is not provided, external entities are reported by the
489 :attr:`DefaultHandler` callback, if provided.
492 .. _expaterror-objects:
494 ExpatError Exceptions
495 ---------------------
497 .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
500 :exc:`ExpatError` exceptions have a number of interesting attributes:
503 .. attribute:: ExpatError.code
505 Expat's internal error number for the specific error. This will match one of
506 the constants defined in the ``errors`` object from this module.
508 .. versionadded:: 2.1
511 .. attribute:: ExpatError.lineno
513 Line number on which the error was detected. The first line is numbered ``1``.
515 .. versionadded:: 2.1
518 .. attribute:: ExpatError.offset
520 Character offset into the line where the error occurred. The first column is
523 .. versionadded:: 2.1
531 The following program defines three handlers that just print out their
534 import xml.parsers.expat
536 # 3 handler functions
537 def start_element(name, attrs):
538 print 'Start element:', name, attrs
539 def end_element(name):
540 print 'End element:', name
542 print 'Character data:', repr(data)
544 p = xml.parsers.expat.ParserCreate()
546 p.StartElementHandler = start_element
547 p.EndElementHandler = end_element
548 p.CharacterDataHandler = char_data
550 p.Parse("""<?xml version="1.0"?>
551 <parent id="top"><child1 name="paul">Text goes here</child1>
552 <child2 name="fred">More text</child2>
555 The output from this program is::
557 Start element: parent {'id': 'top'}
558 Start element: child1 {'name': 'paul'}
559 Character data: 'Text goes here'
562 Start element: child2 {'name': 'fred'}
563 Character data: 'More text'
569 .. _expat-content-models:
571 Content Model Descriptions
572 --------------------------
574 .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
577 Content modules are described using nested tuples. Each tuple contains four
578 values: the type, the quantifier, the name, and a tuple of children. Children
579 are simply additional content module descriptions.
581 The values of the first two fields are constants defined in the ``model`` object
582 of the :mod:`xml.parsers.expat` module. These constants can be collected in two
583 groups: the model type group and the quantifier group.
585 The constants in the model type group are:
588 .. data:: XML_CTYPE_ANY
591 The element named by the model name was declared to have a content model of
595 .. data:: XML_CTYPE_CHOICE
598 The named element allows a choice from a number of options; this is used for
599 content models such as ``(A | B | C)``.
602 .. data:: XML_CTYPE_EMPTY
605 Elements which are declared to be ``EMPTY`` have this model type.
608 .. data:: XML_CTYPE_MIXED
612 .. data:: XML_CTYPE_NAME
616 .. data:: XML_CTYPE_SEQ
619 Models which represent a series of models which follow one after the other are
620 indicated with this model type. This is used for models such as ``(A, B, C)``.
622 The constants in the quantifier group are:
625 .. data:: XML_CQUANT_NONE
628 No modifier is given, so it can appear exactly once, as for ``A``.
631 .. data:: XML_CQUANT_OPT
634 The model is optional: it can appear once or not at all, as for ``A?``.
637 .. data:: XML_CQUANT_PLUS
640 The model must occur one or more times (like ``A+``).
643 .. data:: XML_CQUANT_REP
646 The model must occur zero or more times, as for ``A*``.
651 Expat error constants
652 ---------------------
654 The following constants are provided in the ``errors`` object of the
655 :mod:`xml.parsers.expat` module. These constants are useful in interpreting
656 some of the attributes of the :exc:`ExpatError` exception objects raised when an
659 The ``errors`` object has the following attributes:
662 .. data:: XML_ERROR_ASYNC_ENTITY
666 .. data:: XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF
669 An entity reference in an attribute value referred to an external entity instead
670 of an internal entity.
673 .. data:: XML_ERROR_BAD_CHAR_REF
676 A character reference referred to a character which is illegal in XML (for
677 example, character ``0``, or '``�``').
680 .. data:: XML_ERROR_BINARY_ENTITY_REF
683 An entity reference referred to an entity which was declared with a notation, so
687 .. data:: XML_ERROR_DUPLICATE_ATTRIBUTE
690 An attribute was used more than once in a start tag.
693 .. data:: XML_ERROR_INCORRECT_ENCODING
697 .. data:: XML_ERROR_INVALID_TOKEN
700 Raised when an input byte could not properly be assigned to a character; for
701 example, a NUL byte (value ``0``) in a UTF-8 input stream.
704 .. data:: XML_ERROR_JUNK_AFTER_DOC_ELEMENT
707 Something other than whitespace occurred after the document element.
710 .. data:: XML_ERROR_MISPLACED_XML_PI
713 An XML declaration was found somewhere other than the start of the input data.
716 .. data:: XML_ERROR_NO_ELEMENTS
719 The document contains no elements (XML requires all documents to contain exactly
720 one top-level element)..
723 .. data:: XML_ERROR_NO_MEMORY
726 Expat was not able to allocate memory internally.
729 .. data:: XML_ERROR_PARAM_ENTITY_REF
732 A parameter entity reference was found where it was not allowed.
735 .. data:: XML_ERROR_PARTIAL_CHAR
738 An incomplete character was found in the input.
741 .. data:: XML_ERROR_RECURSIVE_ENTITY_REF
744 An entity reference contained another reference to the same entity; possibly via
745 a different name, and possibly indirectly.
748 .. data:: XML_ERROR_SYNTAX
751 Some unspecified syntax error was encountered.
754 .. data:: XML_ERROR_TAG_MISMATCH
757 An end tag did not match the innermost open start tag.
760 .. data:: XML_ERROR_UNCLOSED_TOKEN
763 Some token (such as a start tag) was not closed before the end of the stream or
764 the next token was encountered.
767 .. data:: XML_ERROR_UNDEFINED_ENTITY
770 A reference was made to a entity which was not defined.
773 .. data:: XML_ERROR_UNKNOWN_ENCODING
776 The document encoding is not supported by Expat.
779 .. data:: XML_ERROR_UNCLOSED_CDATA_SECTION
782 A CDATA marked section was not closed.
785 .. data:: XML_ERROR_EXTERNAL_ENTITY_HANDLING
789 .. data:: XML_ERROR_NOT_STANDALONE
792 The parser determined that the document was not "standalone" though it declared
793 itself to be in the XML declaration, and the :attr:`NotStandaloneHandler` was
794 set and returned ``0``.
797 .. data:: XML_ERROR_UNEXPECTED_STATE
801 .. data:: XML_ERROR_ENTITY_DECLARED_IN_PE
805 .. data:: XML_ERROR_FEATURE_REQUIRES_XML_DTD
808 An operation was requested that requires DTD support to be compiled in, but
809 Expat was configured without DTD support. This should never be reported by a
810 standard build of the :mod:`xml.parsers.expat` module.
813 .. data:: XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING
816 A behavioral change was requested after parsing started that can only be changed
817 before parsing has started. This is (currently) only raised by
818 :meth:`UseForeignDTD`.
821 .. data:: XML_ERROR_UNBOUND_PREFIX
824 An undeclared prefix was found when namespace processing was enabled.
827 .. data:: XML_ERROR_UNDECLARING_PREFIX
830 The document attempted to remove the namespace declaration associated with a
834 .. data:: XML_ERROR_INCOMPLETE_PE
837 A parameter entity contained incomplete markup.
840 .. data:: XML_ERROR_XML_DECL
843 The document contained no document element at all.
846 .. data:: XML_ERROR_TEXT_DECL
849 There was an error parsing a text declaration in an external entity.
852 .. data:: XML_ERROR_PUBLICID
855 Characters were found in the public id that are not allowed.
858 .. data:: XML_ERROR_SUSPENDED
861 The requested operation was made on a suspended parser, but isn't allowed. This
862 includes attempts to provide additional input or to stop the parser.
865 .. data:: XML_ERROR_NOT_SUSPENDED
868 An attempt to resume the parser was made when the parser had not been suspended.
871 .. data:: XML_ERROR_ABORTED
874 This should not be reported to Python applications.
877 .. data:: XML_ERROR_FINISHED
880 The requested operation was made on a parser which was finished parsing input,
881 but isn't allowed. This includes attempts to provide additional input or to
885 .. data:: XML_ERROR_SUSPEND_PE
889 .. rubric:: Footnotes
891 .. [#] The encoding string included in XML output should conform to the
892 appropriate standards. For example, "UTF-8" is valid, but "UTF8" is
893 not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
894 and http://www.iana.org/assignments/character-sets .