emacs: what is C-c % doing in auctex and how can I make it behave better?

C-c % is supposed to be the emacs auctex mode shortcut for commenting out stuff. (There's also C-c ; which comments out the marked region, but that one works). Now sometimes it comments out a single line, sometimes it comments out a line and the ones above it. 开发者_C百科It doesn't seem to have very consistent behaviour.

What I'd really like it to do is comment out the line the cursor is on unless it's on a begin or end tag, in which case comment out the whole environment. (Actually, I'd settle for just understanding the slightly odd behaviour of the comment macro...)

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C-c % runs TeX-comment-or-uncomment-paragraph. For what exactly is considered a paragraph here, see the manual:

Command: TeX-comment-or-uncomment-paragraph
(C-c %) Add or remove % from the beginning of each line in the current paragraph. When removing % characters the paragraph is considered to consist of all preceding and succeeding lines starting with a %, until the first non-comment line.

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Here's a commenting function that does more or less what you want. Uncommenting an environment only works if LaTeX-syntactic-comments is t (and not always very well even then).

(defun LaTeX-comment-environment-or-line (arg)
  "Comment or uncomment the current line.
If the current line is the \\begin or \\end line of an environment, comment
or uncomment the whole environment."
  (interactive "*P")
  (save-match-data
    (save-excursion
      (beginning-of-line)
      (cond
       ((looking-at (concat "\\s-*\\(" TeX-comment-start-regexp "\\)?\\s-*"
                            (regexp-quote TeX-esc) "begin"))
        (let ((begin (point)))
          (goto-char (match-end 0))
          (LaTeX-find-matching-end)
          (TeX-comment-or-uncomment-region begin (point) arg)))
       ((looking-at (concat "\\s-*\\(" TeX-comment-start-regexp "\\)?\\s-*"
                            (regexp-quote TeX-esc) "end"))
        (let ((end (save-excursion (end-of-line) (point))))
          (LaTeX-find-matching-begin)
          (beginning-of-line)
          (TeX-comment-or-uncomment-region (point) end arg)))
       (t
        (TeX-comment-or-uncomment-region
         (point) (save-excursion (end-of-line) (point)) arg))))))