[AUCTeX] font-latex-user-keyword-classes doesn't work

[micheal S]

Hello!

I would like to have syntax highlighting for user defined LaTeX commands.
The auctex manual says, this could be done by setting the variable
font-latex-user-keyword-classes.

I've tried it (via M-x customize-variable), but unfortunately there
was no effect. After setting the variable this way, the corresponding
part of my .emacs file looked like:

(custom-set-variables
;; some other variables
 '(font-latex-user-keyword-classes (quote (("testcommand" nil
(:family "font-latex-sectioning-0-face" :width extra-expanded :weight
extra-bold) noarg))))
)

What did I do wrong?

Is there another way to accomplish the required syntax highlighting for
user defined LaTeX  commands?

When adjusting the variable it was also not clear to me what "font
keywords" I could use.

My auctex version is 11.86.

Thanks in advance
Michael