Not sure which @element pragma is right

[robdodson]

This element uses @element Polymer.CoreFocusable (https://github.com/Polymer/core-focusable/blob/master/core-focusable.js#L8) but core-resizable uses @element CoreResizable (https://github.com/Polymer/core-resizable/blob/master/core-resizable.html#L37). I'm trying to build a doc tool to process these files but I'm not sure which version is the correct one. Is this grey area that we haven't defined yet?

FWIW, the elements that leverage the mixins often refer to them with the Polymer. prefix.
https://github.com/Polymer/paper-button/blob/master/paper-button-base.html#L16
https://github.com/Polymer/paper-tabs/blob/master/paper-tabs.html#L80

@kevinpschaaf @arthurevans @sjmiles