AlternateContentProperty attribute

A new extension point we have added to Blend 3 (based on very popular demand) can be seen put to good use with the Silverlight Chart control - we call it the AlternateContentProperty attribute. Annotating the properties of a control with this attribute allows you to select objects that are set as values (including DepedencyObjects) to be selected in the Blend object tree, thereby exposing a ton of new functionality like the ability to set properties on those objects, edit templates if those objects were FrameworkElements, or set new objects as values of these properties.

Kudos to the Silverlight toolkit team for jumping onto this (I hope a lot more people notice and use this feature in Blend 3 as it really, really enables designers).