jQuery Forum

if ( document.documentElement.contains ) {
	Sizzle.contains = function( a, b ) {
		return a !== b && (a.contains ? a.contains(b) : true);
	};

In the case of a hover event on an SVG element, "a" is the SVG element and "b" is likely some containing DOM element. The first condition fails, naturally. The second also fails, because the SVG element does not have a contains() function. Thus, the function returns "true". Without going into detail, that return value causes a conditional statement in the mouseenter/mouseleave event processor to fail, preventing the handler from being executed.

With a little bit of poking around in the debugger, I found that the alternate implementation of contains() seems to behave as expected in this situation:

} else if ( document.documentElement.compareDocumentPosition ) {
	Sizzle.contains = function( a, b ) {
		return !!(a.compareDocumentPosition(b) & 16);
	};

Knowing that, I was able to resolve my issue by adding a fallback to compareDocumentPosition() to the default implementation. I modified line 5306 in jquery-1.7.js to the following:

return a !== b && (a.contains 
	? a.contains(b) 
	: a.compareDocumentPosition 
		? !!(a.compareDocumentPosition(b) & 16) 
		: true);

All this does is try to use compareDocumentPosition() if contains() does not exist on the element being inspected. In most cases, there should be no change in behavior. In our deviant IE9 case, it allows the hover events to fire as expected.

Hope this helps someone.