Flex组件学习:HttpService

<!-- 载入纯静态的xml数据 -->
<mx:HTTPService id="countriesService" url="http://www.rightactionscript.com/states/xml/countries.xml" />

    <mx:HTTPService result="handleXML(event);" fault="handleFault(event);" id="xmlRPC" resultFormat="e4x"
    	url="http://examples.com/xmlHttpService.jsp" useProxy="false">
	    <mx:request xmlns="">
	        <zipcode>{zipcode.text}</zipcode>
	        <pounds>{weight_lb.text}</pounds>
	    </mx:request>
	</mx:HTTPService>

问题1：对于useProxy="false" 还有 resultFormat="e4x"是什么意思？能否具体就实际说说用法特点？
请求的URL如下：
http://examples.com/xmlHttpService.jsp?zipcode=400&pounds=10

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
    backgroundGradientColors="[0xFFFFFF, 0xAAAAAA]"
    horizontalAlign="left"
    verticalGap="15"
    horizontalGap="15">

    <mx:Script>
        <![CDATA[
            import mx.collections.ArrayCollection;
            import mx.rpc.events.ResultEvent;

            [Bindable]
            private var photoFeed:ArrayCollection;

            private function requestPhotos():void {
                photoService.cancel();
                var params:Object = new Object();
                params.format = 'rss_200_enc';
                params.tags = searchTerms.text;
                photoService.send(params);
            }

            private function photoHandler(event:ResultEvent):void {
                 photoFeed = event.result.rss.channel.item as ArrayCollection;
            }
         ]]>
    </mx:Script>

    <mx:HTTPService id="photoService"
        url="http://api.flickr.com/services/feeds/photos_public.gne"
        result="photoHandler(event)" />

	<mx:HBox>
		<mx:Label text="Flickr tags or search terms:" />
		<mx:TextInput id="searchTerms" />
		<mx:Button label="Search"
			click="requestPhotos()" />
	</mx:HBox>

	<mx:TileList width="100%" height="100%"
		dataProvider="{photoFeed}"
		itemRenderer="FlickrThumbnail">
	</mx:TileList>

</mx:Application>

问题2:代码中的

            private function requestPhotos():void {
                photoService.cancel();
                var params:Object = new Object();
                params.format = 'rss_200_enc';
                params.tags = searchTerms.text;
                photoService.send(params);
            }

它请求的最终URL是个什么样子？