21.4.1 Basic Program Indentation Commands

TAB

Adjust indentation of current line.

LFD

Equivalent to RET followed by TAB (newline-and-indent).

The basic indentation command is TAB, which gives the current line the correct indentation as determined from the previous lines. The function that TAB runs depends on the major mode; it is lisp-indent-line in Lisp mode, c-indent-line in C mode, etc. These functions understand different syntaxes for different languages, but they all do about the same thing. TAB in any programming language major mode inserts or deletes whitespace at the beginning of the current line, independent of where point is in the line. If point is inside the whitespace at the beginning of the line, TAB leaves it at the end of that whitespace; otherwise, TAB leaves point fixed with respect to the characters around it.

Use C-q TAB to insert a tab at point.

When entering a large amount of new code, use LFD (newline-and-indent), which is equivalent to a RET followed by a TAB. LFD creates a blank line, then gives it the appropriate indentation.

TAB indents the second and following lines of the body of a parenthetical grouping each under the preceding one; therefore, if you alter one line’s indentation to be nonstandard, the lines below tend to follow it. This is the right behavior in cases where the standard result of TAB does not look good.

Remember that Emacs assumes that an open-parenthesis, open-brace, or other opening delimiter at the left margin (including the indentation routines) is the start of a function. You should therefore never have an opening delimiter in column zero that is not the beginning of a function, not even inside a string. This restriction is vital for making the indentation commands fast. See Defuns, for more information on this behavior.