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(emacs)Options for Comments

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Options Controlling Comments
----------------------------

   The comment column is stored in the variable `comment-column'.  You
can set it to a number explicitly.  Alternatively, the command `C-x ;'
(`comment-set-column') sets the comment column to the column point is
at.  `C-u C-x ;' sets the comment column to match the last comment
before point in the buffer, and then does a `M-;' to align the current
line's comment under the previous one.

   The variable `comment-column' is per-buffer: setting the variable in
the normal fashion affects only the current buffer, but there is a
default value which you can change with `setq-default'.  Note:
Locals.  Many major modes initialize this variable for the current
buffer.

   The comment commands recognize comments based on the regular
expression that is the value of the variable `comment-start-skip'.
Make sure this regexp does not match the null string.  It may match more
than the comment starting delimiter in the strictest sense of the word;
for example, in C mode the value of the variable is
`"/\\*+ *\\|//+ *""', which matches extra stars and spaces after the
`/*' itself, and accepts C++ style comments also.  (Note that `\\' is
needed in Lisp syntax to include a `\' in the string, which is needed
to deny the first star its special meaning in regexp syntax.  Note:
Regexps.)

   When a comment command makes a new comment, it inserts the value of
`comment-start' to begin it.  The value of `comment-end' is inserted
after point, so that it will follow the text that you will insert into
the comment.  In C mode, `comment-start' has the value `"/* "' and
`comment-end' has the value `" */"'.

   The variable `comment-padding' specifies how many spaces
`comment-region' should insert on each line between the comment
delimiter and the line's original text.  The default is 1, to insert
one space.

   The variable `comment-multi-line' controls how `C-M-j'
(`indent-new-comment-line') behaves when used inside a comment.  If
`comment-multi-line' is `nil', as it normally is, then the comment on
the starting line is terminated and a new comment is started on the new
following line.  If `comment-multi-line' is not `nil', then the new
following line is set up as part of the same comment that was found on
the starting line.  This is done by not inserting a terminator on the
old line, and not inserting a starter on the new line.  In languages
where multi-line comments work, the choice of value for this variable
is a matter of taste.

   The variable `comment-indent-function' should contain a function
that will be called to compute the indentation for a newly inserted
comment or for aligning an existing comment.  It is set differently by
various major modes.  The function is called with no arguments, but with
point at the beginning of the comment, or at the end of a line if a new
comment is to be inserted.  It should return the column in which the
comment ought to start.  For example, in Lisp mode, the indent hook
function bases its decision on how many semicolons begin an existing
comment, and on the code in the preceding lines.