When displaying a combo list in the Moodle home page, the search form at the bottom of the page is not valid WAI AA and US 508:

[WAI 12.4 (AA), US-508-n] Associate form controls with <label> tags using the 'id' attribute:
<input type="text" size="12" name="search" alt="Search courses" value="" />
<input type="submit" value="Search courses" />