USPosition vs. PPosition with Virtual viewports

[Sasha Vasko <sasha aftercode net>]

There is a certain ambiguity in how geometry should be specified by 
user, when Window Manager is supporting virtual viewports. This surfaced 
 as the result of GIMP abuse of USPosition flag which is outlined here 
: http://bugzilla.gnome.org/show_bug.cgi?id=319099
Basically, for user to be able to place , say, a term window into 
arbitrary viewport on the desktop, using just a command-line options - 
geometry must be specified in relation to the desktop origin, there is 
no other way around it. Therefore it is a duty of a Window Manager to 
always treat USPosition in relation to a desktop origin.
On the other hand, as apps itself may not be aware of existence of 
virtual viewports, and even if they do - its not possible to reliably 
take it into consideration - PPosition must always be treated in 
relation to the current viewport's origin.
Now this is not a transparent conclusion for anyone not involved with 
window management to a certain depth, and therefore I suggest that this 
should be clarified in specs under "Desktop/workspace model" subsection 
of Implementation notes.
Anybody wants to comment on that ?

Regards,
Sasha Vasko