Info Catalog elisp: Primitive Indent elisp: Indentation elisp: Region Indent

elisp: Mode-Specific Indent

 
 31.17.2 Indentation Controlled by Major Mode
 --------------------------------------------
 
 An important function of each major mode is to customize the <TAB> key
 to indent properly for the language being edited.  This section
 describes the mechanism of the <TAB> key and how to control it.  The
 functions in this section return unpredictable values.
 
  -- Command: indent-for-tab-command &optional rigid
      This is the command bound to <TAB> in most editing modes.  Its
      usual action is to indent the current line, but it can
      alternatively insert a tab character or indent a region.
 
      Here is what it does:
 
         • First, it checks whether Transient Mark mode is enabled and
           the region is active.  If so, it called ‘indent-region’ to
           indent all the text in the region (Region Indent).
 
         • Otherwise, if the indentation function in
           ‘indent-line-function’ is ‘indent-to-left-margin’ (a trivial
           command that inserts a tab character), or if the variable
           ‘tab-always-indent’ specifies that a tab character ought to be
           inserted (see below), then it inserts a tab character.
 
         • Otherwise, it indents the current line; this is done by
           calling the function in ‘indent-line-function’.  If the line
           is already indented, and the value of ‘tab-always-indent’ is
           ‘complete’ (see below), it tries completing the text at point.
 
      If RIGID is non-‘nil’ (interactively, with a prefix argument), then
      after this command indents a line or inserts a tab, it also rigidly
      indents the entire balanced expression which starts at the
      beginning of the current line, in order to reflect the new
      indentation.  This argument is ignored if the command indents the
      region.
 
  -- Variable: indent-line-function
      This variable’s value is the function to be used by
      ‘indent-for-tab-command’, and various other indentation commands,
      to indent the current line.  It is usually assigned by the major
      mode; for instance, Lisp mode sets it to ‘lisp-indent-line’, C mode
      sets it to ‘c-indent-line’, and so on.  The default value is
      ‘indent-relative’.  Auto-Indentation.
 
  -- Command: indent-according-to-mode
      This command calls the function in ‘indent-line-function’ to indent
      the current line in a way appropriate for the current major mode.
 
  -- Command: newline-and-indent
      This function inserts a newline, then indents the new line (the one
      following the newline just inserted) according to the major mode.
      It does indentation by calling ‘indent-according-to-mode’.
 
  -- Command: reindent-then-newline-and-indent
      This command reindents the current line, inserts a newline at
      point, and then indents the new line (the one following the newline
      just inserted).  It does indentation on both lines by calling
      ‘indent-according-to-mode’.
 
  -- User Option: tab-always-indent
      This variable can be used to customize the behavior of the <TAB>
      (‘indent-for-tab-command’) command.  If the value is ‘t’ (the
      default), the command normally just indents the current line.  If
      the value is ‘nil’, the command indents the current line only if
      point is at the left margin or in the line’s indentation;
      otherwise, it inserts a tab character.  If the value is ‘complete’,
      the command first tries to indent the current line, and if the line
      was already indented, it calls ‘completion-at-point’ to complete
      the text at point (Completion in Buffers).
 

Info Catalog elisp: Primitive Indent elisp: Indentation elisp: Region Indent