Is a url query parameter valid if it has no value?

Question

Is a url like http://example.com/foo?bar valid?

I\'m looking for a link to something official that says one way or the other. A simple yes/no answer or

Answer 1

They're perfectly valid. You could consider them to be the equivalent of the big muscled guy standing silently behind the mob messenger. The guy doesn't have a name and doesn't speak, but his mere presence conveys information.