[ros-users] How to express coupled joints in URDF

Hi,

My robot is composed of various coupled joints for dexterous hands, in which
M joints are driven by N motors.

I tried to find out how to express coupled joints in URDF but couldn't
according to URDF XML reference.
What I only found was PR2-specific <transmission> element. Can this
<transmission> element express coupled joints and relationship between
joints and actuators?

If the element can't express coupled joints, any suggestion to do that will
be appreciated.

TIA

- Yoonsoo