Where is definitely possible attach a panel to `ActionButton`, we
strongly suggest to use always `ToggleButton` instead, see my code
examples in the PR of [anchored panels](https://github.com/mozilla/addon-sdk/pull/1398).

This is because `ActionButton` doesn't provide the required look & feel
defined by UX (see the mockups) where `ToggleButton` does.

When we'll implement the utility function as the one described in the
PR, `ActionButton` won't be listed as suitable target for that reason.

In short, I would avoid to suggest to the devs to use the wrong
component for anchoring panels, especially in examples.