mbbill/undotree — pull request #12 by inkarkat (2012-11-28 10:10:52+00:00)
Title: ENH: Expose plugin state via UndotreeIsVisible().

I have a custom key mapping that toggles different sidebar panels (Tagbar, Project, BufExplorer, and now Undotree) on / off. For that, I need a predicate function that determines whether the plugin is currently active, i.e. shows its window(s). This small public function exposes this information which was previously inaccessible in the script-local objects.