Multiple hash signs in URL

Question

Or maybe you call it "sharp" - the # symbol.

I've came across one instance, where #! and # used simultaneously in a single URL. From reading other articles, including RFC, I can't understand whether that is a legal combination or not. When encountering such page Mozilla browser (Iceweasel in this case) displays the URL as having 2 #'s, while Chrome displays only one, but dies shortly afterwards (the tab containing the page becomes unresponsive and crashes - but it may not be connected).

Now, my question is, is it legal to have both in one URL, is it maybe legal and redundant (should be normalized), or is it just a bug in Mozilla browser? So, suppose I'm making an AJAX request, or trying to navigate the browser history - what should I do, if I encounter this situation?

RFC-3986: http://tools.ietf.org/html/rfc3986#section-3.4 , which should be clarifying it... just in case.

Also: https://developers.google.com/webmasters/ajax-crawling/docs/specification how Google crawlers see things.

Answer 1

The format for a fragment only allows slashes, question marks, and pchars. If you look up the RFC, you'll see that the hash mark is not a valid pchar.

However, browsers will try their best to read non-valid URLs by treating repeat hashes as though they are escaped, as you can see by checking the value of window.location.hash (in IE, Firefox, and Chrome) for

http://www.example.com/hey#foo#bar

which is the same window.location.hash for

http://www.example.com/hey#foo%23bar

Answer 2

It may be legal as @apsillers mentioned. But I would avoid it unless necessary as it can cause a certain confusion concerning the url.

That kind of url:

http://www.example.com/hey#foo#bar

Seems really confusing to me and will be even more confusing to regular users and maybe search engines.