Composit manager question

[Oleg Sukhodolsky]

EWMH defines a _NET_WM_WINDOW_OPACITY hint to tell a composite manager to make
the window translucent. It allows to set just one value for the whole
window. Modern
application require an alpha-mask to be set to make some areas of the
window fully
transparent, others to be semi-transparent and the rest to be fully opaque.
So the questions:
1. Is or will be there a standard way to set the opacity-mask by means
of a hint?
2. If there's no a composite manager running, or the composite manager
doesn't support the
feature (like old and sweet xcompmgr :) ), what is the right way to
set such a mask?
Should the application implement the whole composite manager behavior
and as such
manage all the windows on the user desktop, not only its own windows,
or is it enough to use
some XComposite and/or XRender Extension features for that? What is
the way to detect if
the Composite Manager supports setting an alpha-mask instead of just one value?

Any real code examples may also assist.

Thanks in advance!