This information is part of the Modelica Standard Library maintained by the Modelica Association.

All elementary joints should inherit from this base model, i.e., joints that are directly defined by equations, provided they compute either the rotation object of frame_b from the rotation object of frame_a and from relative quantities (or vice versa), or there is a constraint equation between the rotation objects of the two frames. In other cases, a joint object should inherit from Interfaces.PartialTwoFrames (e.g., joint Spherical, because there is no constraint between the rotation objects of frame_a and frame_b or joint Cylindrical because it is not an elementary joint).

This partial model provides two frame connectors, a "Connections.branch" between frame_a and frame_b, access to the world object and an assert to check that both frame connectors are connected.