I'll explain about "id" references a little further, as I
have come to understand:
Say you put an id="someValue" into an mxml tag. When the mxml
is generated into AS (the first step in compilation), the generator
creates an instance variable named "someValue" that contains a
reference to the control generated by the tag. This is why you can
reference a control by its id.
When you instantiate controls in code, you have to do this