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(elisp)Filling

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Filling
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   "Filling" means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width.  Additionally, lines can be "justified", which means
inserting spaces to make the left and/or right margins line up
precisely.  The width is controlled by the variable `fill-column'.  For
ease of reading, lines should be no longer than 70 or so columns.

   You can use Auto Fill mode (Note: Auto Filling) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled.  Then you must fill the text explicitly.

   Most of the commands in this section return values that are not
meaningful.  All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(Note: Margins).  If the current justification style is `none', the
filling functions don't actually do anything.

   Several of the filling functions have an argument JUSTIFY.  If it is
non-`nil', that requests some kind of justification.  It can be `left',
`right', `full', or `center', to request a specific style of
justification.  If it is `t', that means to use the current
justification style for this part of the text (see
`current-justification', below).  Any other value is treated as `full'.

   When you call the filling functions interactively, using a prefix
argument implies the value `full' for JUSTIFY.

 - Command: fill-paragraph justify
     This command fills the paragraph at or after point.  If JUSTIFY is
     non-`nil', each line is justified as well.  It uses the ordinary
     paragraph motion commands to find paragraph boundaries.  Note:
     Paragraphs.

 - Command: fill-region start end &optional justify nosqueeze to-eop
     This command fills each of the paragraphs in the region from START
     to END.  It justifies as well if JUSTIFY is non-`nil'.

     If NOSQUEEZE is non-`nil', that means to leave whitespace other
     than line breaks untouched.  If TO-EOP is non-`nil', that means to
     keep filling to the end of the paragraph--or the next hard
     newline, if `use-hard-newlines' is enabled (see below).

     The variable `paragraph-separate' controls how to distinguish
     paragraphs.  Note: Standard Regexps.

 - Command: fill-individual-paragraphs start end &optional justify
          citation-regexp
     This command fills each paragraph in the region according to its
     individual fill prefix.  Thus, if the lines of a paragraph were
     indented with spaces, the filled paragraph will remain indented in
     the same fashion.

     The first two arguments, START and END, are the beginning and end
     of the region to be filled.  The third and fourth arguments,
     JUSTIFY and CITATION-REGEXP, are optional.  If JUSTIFY is
     non-`nil', the paragraphs are justified as well as filled.  If
     CITATION-REGEXP is non-`nil', it means the function is operating
     on a mail message and therefore should not fill the header lines.
     If CITATION-REGEXP is a string, it is used as a regular
     expression; if it matches the beginning of a line, that line is
     treated as a citation marker.

     Ordinarily, `fill-individual-paragraphs' regards each change in
     indentation as starting a new paragraph.  If
     `fill-individual-varying-indent' is non-`nil', then only separator
     lines separate paragraphs.  That mode can handle indented
     paragraphs with additional indentation on the first line.

 - User Option: fill-individual-varying-indent
     This variable alters the action of `fill-individual-paragraphs' as
     described above.

 - Command: fill-region-as-paragraph start end &optional justify
          nosqueeze squeeze-after
     This command considers a region of text as a single paragraph and
     fills it.  If the region was made up of many paragraphs, the blank
     lines between paragraphs are removed.  This function justifies as
     well as filling when JUSTIFY is non-`nil'.

     In an interactive call, any prefix argument requests justification.

     If NOSQUEEZE is non-`nil', that means to leave whitespace other
     than line breaks untouched.  If SQUEEZE-AFTER is non-`nil', it
     specifies a position in the region, and means don't canonicalize
     spaces before that position.

     In Adaptive Fill mode, this command calls `fill-context-prefix' to
     choose a fill prefix by default.  Note: Adaptive Fill.

 - Command: justify-current-line &optional how eop nosqueeze
     This command inserts spaces between the words of the current line
     so that the line ends exactly at `fill-column'.  It returns `nil'.

     The argument HOW, if non-`nil' specifies explicitly the style of
     justification.  It can be `left', `right', `full', `center', or
     `none'.  If it is `t', that means to do follow specified
     justification style (see `current-justification', below).  `nil'
     means to do full justification.

     If EOP is non-`nil', that means do left-justification if
     `current-justification' specifies full justification.  This is used
     for the last line of a paragraph; even if the paragraph as a whole
     is fully justified, the last line should not be.

     If NOSQUEEZE is non-`nil', that means do not change interior
     whitespace.

 - User Option: default-justification
     This variable's value specifies the style of justification to use
     for text that doesn't specify a style with a text property.  The
     possible values are `left', `right', `full', `center', or `none'.
     The default value is `left'.

 - Function: current-justification
     This function returns the proper justification style to use for
     filling the text around point.

 - User Option: sentence-end-double-space
     If this variable is non-`nil', a period followed by just one space
     does not count as the end of a sentence, and the filling functions
     avoid breaking the line at such a place.

 - Variable: fill-paragraph-function
     This variable provides a way for major modes to override the
     filling of paragraphs.  If the value is non-`nil',
     `fill-paragraph' calls this function to do the work.  If the
     function returns a non-`nil' value, `fill-paragraph' assumes the
     job is done, and immediately returns that value.

     The usual use of this feature is to fill comments in programming
     language modes.  If the function needs to fill a paragraph in the
     usual way, it can do so as follows:

          (let ((fill-paragraph-function nil))
            (fill-paragraph arg))

 - Variable: use-hard-newlines
     If this variable is non-`nil', the filling functions do not delete
     newlines that have the `hard' text property.  These "hard
     newlines" act as paragraph separators.