SDF Joint/Link additional info (Electronics + Mechanical fit)

I am working on an application to make it easier to cooperate on open robotics hardware. In order to keep track of what (still) fits together I need a way to store information about how the mechanical parts attach together and what electrical requirements and capabilities that a module/link have. It would be great if i could append this information to a SDF model of a robot without violating the standard.

Any suggestions?