Box2D User data for shapes?

Hello. I wanted to set the UserData for shapes on a body. (I have already done so for the bodys). However I am having trouble finding the command. The manual indicates that you can set user data for shapes - but no command is listed in the list of functions. I have tried shapeDef.SetUserData(data) - but it says 'SetUserData' not found.

How do I set the UserData for a shape? Thank you very much.