xml.length();

- xml data     

<main>
  
</main>

<main>
  
  
</main>

<main>
  
  
  
</main>

<main>
  
  
  
  
</main>

- Action Script     

var xml:XML;
var xmlLoader:URLLoader = new URLLoader();
xmlLoader.load(new URLRequest("xmlData.xml"));
xmlLoader.addEventListener(Event.COMPLETE, xmlComplete);

function xmlComplete (e:Event):void{
    xml = new XML(e.target.data);

    setting();
}

function setting():void{
    trace(xml.main.length())          // 4;
    trace(xml.main[0].length())      // 1;
    trace(xml.main.sub.length())    // 10;  -->  이런식으로 sub의 총 갯수를 알아낼수도 있다.
}