http://www.fgm.cc/learn/lesson8/01.html上面是源碼上面這段js代碼中的var get = {?? ?byId: function(id) {?? ??? ?return typeof id === "string" ? document.getElementById(id) : id?? ?},?? ?byClass: function(sClass, oParent) {?? ??? ?var aClass = [];?? ??? ?var reClass = new RegExp("(^| )" + sClass + "( |$)");?? ??? ?var aElem = this.byTagName("*", oParent);?? ??? ?for (var i = 0; i < aElem.length; i++) reClass.test(aElem[i].className) && aClass.push(aElem[i]);?? ??? ?return aClass?? ?},?? ?byTagName: function(elem, obj) {?? ??? ?return (obj || document).getElementsByTagName(elem)?? ?}這一段怎么解釋呢？請幫我解釋一下，謝謝。