Skipping Windows in ALT-TAB Task List?

[Adam Kessel]

Is it Openbox's job to keep track of which windows belong in the alt-tab
cycle list?  Is there an easy way to specify which windows should be
skipped when the programs themselves provide no such functionality? 
E.g., gkrellm knows it shouldn't be in the alt-tab list, but xmms does
not appear to have any way to specify that.
-- 
Adam Kessel
http://adam.rosi-kessel.org