(This is from the discussion at the UI controls offsite.)

There should be a developer/debugging-level API to provide better
control over the pulse. One function would be to disable the automatic
pulse. Another would be to trigger a pulse manually. Still another might
be to enable some kind of callback or notification that a pulse has
occurred. This is useful for debugging, and it would be helpful to have
this integrated into a tool so that one could see what's going on during
the layout pass etc.

There is also the desire to have this be in a "single call". (Sorry, that's
just the notes from the flipchart; I'm not exactly sure what that means.)