IRSSI style focus

Irssi-style window switching is the use of a modifier key + a number key to switch to a specific window. For example, one could set up W-3 to switch to the third open window. This is easily accomplished in Openbox by setting up keybindings to execute this little external focus-switching program like so:

<keybind key="W-1">
  <action name="execute">
    <execute>irssi-focus 0</execute>
  </action>
</keybind>
<keybind key="W-2">
  <action name="execute">
    <execute>irssi-focus 1</execute>
  </action>
</keybind>

and so on.