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(elisp)Mode-Specific Indent

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Indentation Controlled by Major Mode
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   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.

 - Variable: indent-line-function
     This variable's value is the function to be used by <TAB> (and
     various commands) to indent the current line.  The command
     `indent-according-to-mode' does no more than call this function.

     In Lisp mode, the value is the symbol `lisp-indent-line'; in C
     mode, `c-indent-line'; in Fortran mode, `fortran-indent-line'.  In
     Fundamental mode, Text mode, and many other modes with no standard
     for indentation, the value is `indent-to-left-margin' (which is the
     default value).

 - 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: indent-for-tab-command
     This command calls the function in `indent-line-function' to indent
     the current line; however, if that function is
     `indent-to-left-margin', `insert-tab' is called instead.  (That is
     a trivial command that inserts a tab character.)

 - 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 the current `indent-line-function'.
     In programming language modes, this is the same thing <TAB> does,
     but in some text modes, where <TAB> inserts a tab,
     `newline-and-indent' indents to the column specified by
     `left-margin'.

 - 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).

     This command does indentation on both lines according to the
     current major mode, by calling the current value of
     `indent-line-function'.  In programming language modes, this is
     the same thing <TAB> does, but in some text modes, where <TAB>
     inserts a tab, `reindent-then-newline-and-indent' indents to the
     column specified by `left-margin'.