elisp - emacs: is there a clear example of multi-line font-locking?

Question

Some background, I'm comfortable with Emacs Lisp, and have written lots of lines of it. However I've never written a major mode, so I'm fairly new to how the font-locking mechanism works.

For my current project, I'd like to add inlined javascript and css highlighting to html-mode. Currently, I do this with MMM-mode, but it's bulky and I don't use other features of it, so I'd just like to make a minor-mode or even just a hack that I can add to the sgml-mode-hook to just do the highlighting.

I've found this section of the manual, which sorely lacks an example, and this emacswiki page of broken code.

Can someone show me a clear example of how this is can be done?

EDIT: I should clarify that I don't want to see mode-specific font-locking within the javascript/css chunks. The only requirement is that I'm able to see the chunks by applying a different face to them.

Answer 1

In the example below, I use the "anchored" form of font-lock keywords, it allows you to search more than the current line. The "trick" is that the "pre" hook do two things: 1) it allows you to position the point to the start of the search and 2) it allows you to limit the search by returning the end-position. In the example below, I have used the second property.

Note that this is only a proof-of-concept. You will need to make sure that the font-lock-multiline variable and the font-lock keywords are applied to the correct buffer.

(defun my-end-of-paragraph-position (&rest foo)
  "Return position of next empty line."
  (save-excursion
    (while (not (or (eobp)             ; Stop at end of buffer.
                    (and (bolp)        ; Or at an empty line.
                         (eolp))))
      (forward-line))
    (point)))

(setq font-lock-multiline t)

(font-lock-add-keywords nil
                        '(("^FOO"
                           (0 font-lock-keyword-face)  ;; Face for FOO
                           ("BAR"
                            (my-end-of-paragraph-position)
                            nil
                            (0 font-lock-variable-name-face)))))

Below, the first two lines of BAR will be highlighted, but not the last:

FOO BAR BAR BAR BAR
BAR BAR BAR BAR

BAR BAR BAR BAR