Query源码 — after方法
after方法定义在jQuery.prototype

after: function() {if ( this[0] && this[0].parentNode ) {return this.domManip(arguments, false, function( elem ) {this.parentNode.insertBefore( elem, this.nextSibling );});} else if ( arguments.length ) {var set = this.pushStack( this, "after", arguments );set.push.apply( set, jQuery(arguments[0]).toArray() );return set;}}