in static/assets/js/modernizr.js [547:558]
tests['multiplebgs'] = function() {
// Setting multiple images AND a color on the background shorthand property
// and then querying the style.background property value for the number of
// occurrences of "url(" is a reliable method for detecting ACTUAL support for this!
setCss('background:url(https://),url(https://),red url(https://)');
// If the UA supports multiple backgrounds, there should be three occurrences
// of the string "url(" in the return value for elemStyle.background
return (/(url\s*\(.*?){3}/).test(mStyle.background);
};