When specifying --actions, it is sometimes important to be able to specify which instance of feh they are attached to.

For example, I want to write an action which allows me to do simple multiple selection within the current filelist. (essentially building a sub-filelist, which I can later perform an action on.). So it's important to identify which feh instance the selection belongs to, that makes it possible to associate the selection with feh instance correctly, and also for the later action to use the correct selection.

I think process id is suitable for identifying sessions, and '%V' is fairly logical in association with the existing %v; failing that, %I (as in 'session ID') works.

I don't know how your multiwindow setup works -- if that's all in the one process, I guess the window XID would be more appropriate. For now, I've implemented a very simple patch mapping %V to process id, and attached it to this issue.