message: Adding comment block describing "active side" concept for FaceElementTransformations objects
diff: @@ -361,6 +361,21 @@ public:
  FaceElementTransformations() : side(2) {}
  + /** FaceElementTransformations objects are often used when
  + performing the surface integrals on the interfaces between
  + elements needed by Discontinuous Galerkin methods. Since the
  + fields are generally multivalued on such interfaces it is
  + important to specify which neighboring element should supply
  + the field values. This is controlled by setting the "active
  + side" in the FaceElementTransformations object.
  +
  + Possible values for s are 0, 1, and 2:
  + 0 - Set Elem1No as the active side
  + 1 - Set Elem2No as the active side
  + 2 - Choose the active side automatically. This selects Elem1No
  + unless Elem2No exists and has a lower attribute number than
  + Elem1No.
  + */
  int SetActiveSide(int s);
  int GetActiveSide() const { return side; }
  