Yeah, E4X Can Do (Some Of) That

In brief, you can use an XMLList as a container, literally its <></>. There is a toXMLString(), and you can set properties on the xml object to change how it is serialized. Lastly, elements can be created using the bracket inclusion mechanism. Also works for attributes and attribute values.

The code:

function buildItems() {
  return <>
           <item>Hello</item>
           <item>World!</item>
         </>;
}
var doc = <mydocument>{buildItems()}</mydocument>;

print( "appended child elements")
print( doc );

print();
print( "to xml string")
print( doc.toXMLString() );

var foo = "foo";

doc.item += <{foo}/>

print();
print( "dyanmic element creation??")
print( doc );

The output:

  appended child elements
  <mydocument>
    <item>Hello</item>
    <item>World!</item>
  </mydocument>

  to xml string
  <mydocument>
    <item>Hello</item>
    <item>World!</item>
  </mydocument>

  dyanmic element creation??
  <mydocument>
    <item>Hello</item>
    <item>World!</item>
    <foo/>
  </mydocument>

Also see Deciphering E4X and the 1060 E4X Tutorial.