[Swftools-common] ST_REMOVEOBJECT vs. ST_REMOVEOBJECT2

[wolfgang-steiner]

As I explored/tested SwfDump further I found out that in all my test SWFs,
objects are beeing removed by ST_REMOVEOBJECT2 all the time, which seems
to remove all objects from a layer (aka. depth) and then moves all upper
objects (regarding depth) down one layer (to fill the now empty layer up).

An example:
I have 3 objects in my SWF. Each is placed at a seperate depth layer on
frame 1.
At frame 5 the second of the objects is removed ("REMOVEOBJECT2 removes
object from depth 0002") without any ID specified (therefore I assumed
that it erases the entire '2' layer). The next step in the SWF moves the
third object down one depth layer (PLACEOBJECT2 places id 0002 at depth
0002) and removes/clears the third layer, where the object was originally
located before the removal.

This is just my theory how removing/adding objects is done without knowing
any IDs ---> per layer. This throws up 3 questions:

a) Is it possible to have more than 1 object per depth layer? I assume
it's not.

b) If my theory is right, what is the sense of REMOVEOBJECT(1) and
PLACEOBJECT(1), or when are they used?

c) totally unrelated to the above: is it right that each object has it's
unique ID, regardless which kind of object it is?
Meaning, is it right that for example a sound can never have an equal ID
to an image (DEFINEBITSJPEG2) or a shape (DEFINESHAPE), etc. ?

Thanks a lot for any help,

Greetings
Wolfgang aka. stoneCold