How do I get the alias string of a class in AS3?

var alias:String = 'models.User';
registerClassAlias(alias, models.User);

// If I have the alias, then
// I can get the class like this:
var klass:Class = flash.net.getClassByAlias(alias);

// How do I do the reverse
// (get the alias from the class)?
//
// I want to do this, but I can't find a
// 'getAliasByClass' function.
alias = getAliasByClass(klass);

alias = flash.utils.getQualifiedClassName( klass );
// should return: "models::User"

override protected function encodeComplex(o:Object, b:IBinary, context:IContext=null):void
{
		var desc:XML = describeType(o);
		var classAlias:String = desc.@alias;
		//...
}