Should address //sensor/imu/orientation_reference_frame/custom_rpy/[@parent_frame] in the pose frame semantics proposal

[azeey]

The spec describes //sensor/imu/orientation_reference_frame/custom_rpy/[@parent_frame] as

Name of parent frame which the custom_rpy transform is defined relative to. It can be any valid fully scoped Gazebo Link name or the special reserved "world" frame. If left empty, use the sensor's own local frame.

The current of pose frame semantics proposal does not include this attribute.