Summary info potentially misleading

[sjmiles]

This event will be fired when they become showing after having been hidden, when they are resized explicitly by another resizable, or when the window has been resized.

Users sometimes take this to mean that adding this behavior will provide detection for arbitrary visibility changes (as opposed to being able to receive visibility change notifications from explicit broadcasts).

[fearlessbryan]

For example: http://stackoverflow.com/questions/35785548/polymer-ironresizablebehavior-iron-resize-event-not-fired-when-resizable-eleme

[mercmobily]

+1, I also had to look at the code to really get what this behaviour did!