You mean like section 10.16 in draft-ietf-http-v10-spec-04.txt, which
specifies that the User-Agent header should contain one or more
products or comments, and section 3.7 of the same document, which
specifies that a product is a product-token, a slash, and a
product-version? Token and comment are likewise defined in that
document.
Of course, until people either 1) stop doing content negotiation based
on user-agent, or 2) start paying attention to browsers other than
Moscape, this is immaterial - authors (and users) of browsers that are
going to lie about the user-agent in order to get the best document
they can.
<mike