Focus on OS X

Is there any way to make editing-callback fire when the user first  
focuses on a text-input-pane? The behavior on Mac differs from Windows  
and Motif since it requires the user to make a change before editing  
has been initiated. Will I have to iterate over all text input panes  
to find the one with focus or is there a more straightforward solution  
that I'm missing?

Thanks,
Evan