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elisp: Standard Regexps

 
 33.8 Standard Regular Expressions Used in Editing
 =================================================
 
 This section describes some variables that hold regular expressions used
 for certain purposes in editing:
 
  -- User Option: page-delimiter
      This is the regular expression describing line-beginnings that
      separate pages.  The default value is ‘"^\014"’ (i.e., ‘"^^L"’ or
      ‘"^\C-l"’); this matches a line that starts with a formfeed
      character.
 
    The following two regular expressions should _not_ assume the match
 always starts at the beginning of a line; they should not use ‘^’ to
 anchor the match.  Most often, the paragraph commands do check for a
 match only at the beginning of a line, which means that ‘^’ would be
 superfluous.  When there is a nonzero left margin, they accept matches
 that start after the left margin.  In that case, a ‘^’ would be
 incorrect.  However, a ‘^’ is harmless in modes where a left margin is
 never used.
 
  -- User Option: paragraph-separate
      This is the regular expression for recognizing the beginning of a
      line that separates paragraphs.  (If you change this, you may have
      to change ‘paragraph-start’ also.)  The default value is
      ‘"[ \t\f]*$"’, which matches a line that consists entirely of
      spaces, tabs, and form feeds (after its left margin).
 
  -- User Option: paragraph-start
      This is the regular expression for recognizing the beginning of a
      line that starts _or_ separates paragraphs.  The default value is
      ‘"\f\\|[ \t]*$"’, which matches a line containing only whitespace
      or starting with a form feed (after its left margin).
 
  -- User Option: sentence-end
      If non-‘nil’, the value should be a regular expression describing
      the end of a sentence, including the whitespace following the
      sentence.  (All paragraph boundaries also end sentences,
      regardless.)
 
      If the value is ‘nil’, as it is by default, then the function
      ‘sentence-end’ constructs the regexp.  That is why you should
      always call the function ‘sentence-end’ to obtain the regexp to be
      used to recognize the end of a sentence.
 
  -- Function: sentence-end
      This function returns the value of the variable ‘sentence-end’, if
      non-‘nil’.  Otherwise it returns a default value based on the
      values of the variables ‘sentence-end-double-space’ (
      Definition of sentence-end-double-space),
      ‘sentence-end-without-period’, and ‘sentence-end-without-space’.
 

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