@c This is part of the Emacs manual.
@c Copyright (C) 2023 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Alignment
@chapter Alignment
@cindex alignment

  @dfn{Alignment} is the process of adjusting whitespace in a sequence
of lines such that in all lines certain parts begin at the same
column.  This is usually done to enhance readability of a piece of
text or code.  The classic example is aligning a series of assignments
in C-like programming languages:

@example
int a = 1;
short foo = 2;
double blah = 4;
@end example

Is commonly aligned to:

@example
int    a    = 1;
short  foo  = 2;
double blah = 4;
@end example

@findex align
  You can use the command @kbd{M-x align} to align lines in the
current region.  This command knows about common alignment patterns
across many markup and programming languages.  It encodes these
patterns as a set of @dfn{alignment rules}, that say how to align
different kinds of text in different contexts.

@kbd{M-x align} splits the region into a series of @dfn{sections},
usually sequences of non-blank lines, and aligns each section
according to a matching alignment rule by expanding or contracting
stretches of whitespace.  If you call this command with a prefix
argument (@kbd{C-u M-x align}), it enables more alignment rules that
are often useful but may sometimes be too intrusive.  For example, in
a Lisp buffer with the following form:

@lisp
(set-face-attribute 'mode-line-inactive nil
                    :box nil
                    :background nil
                    :underline "black")
@end lisp

Typing (@kbd{C-u M-x align}) yields:

@lisp
(set-face-attribute 'mode-line-inactive nil
                    :box                nil
                    :background         nil
                    :underline          "black")
@end lisp

@vindex align-indent-before-aligning
  If the user option @code{align-indent-before-aligning} is
non-@code{nil}, Emacs indents the region before aligning it with
@kbd{M-x align}.  @xref{Indentation}.

@vindex align-to-tab-stop
  The user option @code{align-to-tab-stop} says whether aligned parts
should start at a tab stop (@pxref{Tab Stops}).  If this option is
@code{nil}, @kbd{M-x align} uses just enough whitespace for alignment,
disregarding tab stops.  If this is a non-@code{nil} symbol, @kbd{M-x
align} checks the value of that symbol, and if this value is
non-@code{nil}, @kbd{M-x align} aligns to tab stops.