function $class(classname, parentid){

	var targets=[],kids=[];

	if(parentid){
	    var parent=document.getElementById(parentid);
	    kids=parent.getElementsByTagName("*");
	}else{
	    kids=document.getElementsByTagName("*");
	}

	for(var i=0;i<kids.length;i++){

        if(kids[i].className.indexOf(classname)!=-1){
            targets.push(kids[i]);
        }
	        
	}
    
    return targets;//返回目标元素数组
}