The expandable icon buttons and the slick white limit-select that are used in the omni-present TableView widget are recognized at a core part of the Piwik UI. If someone develops a new (non-table) widget, he/she definitely wants to use the same user interface elements.
Currently, there seems to be no way of doing this except coping the entire mark-up and behaviour of the TableView buttons. I think it would be much nicer to have the button UI clearly separated from the TableView.
Thanks for the suggestion.
Unfortunately not quite trivial so decreasing priority - Greg copy pasting the code is OK for now, thanks!
Wont fix for now, but when we have more use case or build up the framework more we will re-open :)