UnexpectedRunTimeErrors.as

// This constant is set to the fully qualified class name for Vector
private static const VECTOR_CLASS:String = "__AS3__.vec::Vector";
 
// Use flash.utils.describeType() on the input, and verify type 
// of the object is a Vector class. This is probably fairly
// expensive, a valid point to my argument.
public static function isVector(vector:*):Boolean {     
    var type:String = flash.utils.describeType(vector).@name;
    return type.indexOf(VECTOR_CLASS) != -1;
}