In a Drupal 6 site, I want to override theme_select but my mymodule_select is never called. I tried instead making mymodule_form_element because theme_select anyway calls that for its output, but that custom function is also never called.

The reason, BTW, that I want to do this is to be able to apply a class to some <option> tags.

Any ideas what I am doing wrong?

Thanks.