Is there an option to focus a widget?

[MarcWeber]

WMII had a bar allowing to send some words, and allow it to select or enter a new word. I wanted to get the same feature for yabai eventually using wunderlist as bar.
So what I want is give the bar the focus, tab complete some names. If selected/typed name doesn't exist create new space and switch to it. Yabai itself doesn't seem to find the wunderlist widget in its window list. So can't use it's --focus feature. Is there a different simple known way or would .focus() (JS) be enough?