Make sure that if an attribute contains < or >, a warning is given; these

Make sure that if an attribute contains < or >, a warning is given; these
warnings aren't pedantic because (1) if it's a templating directive, it
might expand into something containing a real < and/or >, and (2) if it
contains >, the browser will close the current tag, and (3) if it contains
< and the browser knows what "SGML closed start tags" are (e.g., Mozilla),
the browser will also close the current tag.