[doxygen] Respond to tkuchida's feedback.
[doxygen] Respond to tkuchida's feedback.

[ci skip]
opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core