Thread Subject: mexSubsReference mexSubsAssign

Who knows what the subs parameter in the following (undocumented-?)
functions means?

extern mxArray *mexSubsReference(
      const mxArray *prhs,
      const mxArray *subs[],
      int nsubs
      );

mexSubsAssign(
      mxArray *plhs,
      const mxArray *prhs,
      const mxArray *subs[],
      int nsubs
      );

Whould you give me an example?