Pattern is by default a normal string that is matched precisely (but without regard to case, except in the case of pickaxe). However, when you check the re checkbox, the pattern entered is recognized as the POSIX extended regular expression (also case insensitive).

commit

The commit messages and authorship information will be scanned for the given pattern.

author

Name and e-mail of the change author and date of birth of the patch will be scanned for the given pattern.

committer

Name and e-mail of the committer and date of commit will be scanned for the given pattern.