Add comment to inform that results from virtual calculation methods are cached by the Frame.
Add comment to inform that results from virtual calculation methods are cached by the Frame.

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