According to the DTD, HREF is optional -- mostly because there's
no way to express in SGML the sentiment "either the NAME attribute
or the HREF attribute must be present."
>From the HTML spec:
http://info.cern.ch/hypertext/WWW/MarkUp/Elements/A.html
All attributes are optional, although one of NAME and HREF is necessary
for the anchor to be useful.
It's reasonable to change that to say:
All attributes are optional, although one of NAME, HREF, or URN is necessary
for the anchor to be useful.
Whereas in the near term, an A tag with a URN attribute
but no HREF attribute is useless to most of the community,
I suggest that you use the URN for the lasting name, but for the
benefit of existing clients, you include a redundant
HREF.
Dan