Common functions /*
var insertRule=(function(){
if( document.styleSheets && document.styleSheets.length ) {
var styleSheet=document.styleSheets[0];
return function(keyframes){ styleSheet.insertRule( keyframes, 0 ); }
}else{
var s = document.createElement( 'style' );
document.head.appendChild( s );
return function(keyframes){ s.innerHTML = s.innerHTML + keyframes };
}
})();
function(duration){
		if(duration===0) throw new Error('Duration must not be === 0');
		if(!S.isString(duration)) return duration;
		return duration.contains('ms') ? parseInt(duration, 10) : parseInt(duration, 10) * 1000; 
	}