While rewriting a page on the Oddmuse site, I found this little nugget of useful information that I don’t want to loose:
All elements other than those declared in the DTD as EMPTY must have an end tag. Elements that are declared in the DTD as EMPTY can have an end tag or can use empty element shorthand (see Empty Elements). ¹
The content model for the a element is not EMPTY. ² Therefore, you need an explicit closing tag for a elements, even if you’re just adding a named anchor:
<a name="foo"></a>
#Web