Getting pid of focus window

[Bill Spitzak]

I expect Wayland will add a "attach this blob of data to this 
window+key" similar to X window properties, for IPC to the compositor 
and other software.

The question is whether software is going to be required to keep these 
things up to date for information that Wayland must know anyway. 
Requiring the compositor to track the focus changes and set an attribute 
on a window so other programs can see which window has focus seems 
wasteful and unreliable, since Wayland is using this information itself 
anyway.

But rather than adding a "give me the focus window" api, it may make a 
lot of sense for Wayland to automatically update a set of properties. Ie 
there would always be a "which window has focus" property without the 
compositor having to set it. Instead Wayland sets it internally. Sort of 
like the /proc filesystem.

PS: Please make the properties be UTF-8 text only (well actually byte 
streams with some non-enforced encouragement that they be UTF-8 text). 
No data types. Programs can parse and this is much more user and 
programmer friendly.