title: What characters are allowed in an HTML attribute name?
body: <p>In HTML attribute <strong>name=value</strong> pairs, what are the characters allowed for the 'name' portion? ..... Looking at some <a href="http://www.w3.org/TR/REC-html40/index/attributes.html" rel="noreferrer">common attributes</a> it appears that only letters (a-z and A-Z) are used, but what other chars could be allowed as well?...  maybe digits (0-9), hyphens (-), and periods (.) ... is there any spec for this?</p>