HTML properties without quotation marks?

Answer 1

You can omit the quotes from an attribute value if the value consists of the following characters only (cf to the technical concept of name):

letters of the English alphabet (A to Z, a to z)
digits (0 to 9)
periods .
hyphens -

Thus, WIDTH=80 and ALIGN=CENTER are legal shorthands for WIDTH="80" and ALIGN="CENTER". A reference to a URL like HREF=foo.html is acceptable, but in general URLs must be quoted when used in attributes, e.g. HREF="http://www.hut.fi/". - Some browsers are more permissive. Some browsers may even accept elements with a starting quote but without any closing quote. Such use is very bad practise.

refer http://www.cs.tut.fi/~jkorpela/HTML3.2/3.4.html