Sketch for MXML building problem - this I understand.

FSM.mxml

<?xml version="1.0"?>
<fsm:FSMDeclaration
    xmlns:fx="http://ns.adobe.com/mxml/2009"
    xmlns:fsm="fsm.*"
    initial="{s1}">

    <fsm:State id="s1"/>
    <fsm:State id="s2"/>

</fsm:FSMDeclaration>

FSMDeclaration.as

package fsm {

    [DefaultProperty("values")]

    public class FSMDeclaration {

        public var initial:IState;

        public var values:Array = [];

    }
}