I have created several custom widgets, modeled from the default widgets' code. The widgets all work fine, and I've been using them in production for awhile.
I've been working with the new Customizer API, and I just discovered the "shift-click to edit" functionality. However, none of my custom widgets work properly with this feature.
I'm aware of the current limitation of needing the widgets panel to be open for the clicked widget to properly bring focus in the panel: the default widgets are working as they should.
I've been scouring over source to try and figure out how this works, with no luck.
What controls this behavior when registering a widget?