First off, thank you Olivier for adding in switch_window_key and clientSwitchWindow().  I think more WM's need to think about switching windows within an application, especially as users spawn an unthinkable number of windows (guilty as charged when it comes to Terminal).

However, switch_window_key's behavior is really odd at this point.  Firstly, it only cycles forward.  Meaning, if you invoke it once (<Super>+<Tab> by default), release <Super>, then invoke it again, it will only select the next forward window.  It will not cycle back to the last window a-la <Alt>+<Tab>.

Also, the name of the command is awfully close to the cycling of entire applications and application windows which is cycle_windows_key.  So I'm not sure of the implications here when it comes to the eventual implementation of a more cycle-like behavior.  Perhaps switch_window_key should become cycle_subwindow_key?  Perhaps introduce new functions for these behaviors?

Either way, only being able to advance windows without any cycle memory or reverse capability is bothersome.  If I had more time and knowledge of your codebase I'd take a stab at a patch but alas I have neither.