Broke up Y.Attribute into: Y.AttributeCore (Attribute without Events, or lesser used features) Y.AttributeEvents (AttributeEvent support) Y.AttributeExtras (Attribute lesser used features) Y.Attribute remains 100% backwards compatible. Attribute/Base/Widget/Plugin/App/Node/WidgetParentChild tests all pass. Y.State's internal data structure was changed. If you're accessing the private _state.data's fields directly, you'll need to change code. HISTORY.md has details.