It would be really, really nice to have a require_css function that works a bit like require_js. It would make it much easier for plugins and patches that need to get stylesheet links into the header, but which don't make the print_header call directly. See http://cvs.moodle.org/contrib/plugins/admin/report/userroles/index.php?revision=1.2&view=markup for an implementation. You aslo need to change the $meta .= "\n".require_js(); line in print_header.