[jQuery] Re: Bug with JQuery is?

http://docs.jquery.com/Traversing/is#expr

"If no element fits, or the expression is not valid, then the response
will be 'false'. Note: Only simple expressions are supported. Complex
expressions, such as those containing hierarchy selectors (such as +,
~, and >) will always return 'true'. filter is used internally,
therefore all rules that apply there apply here, as well."