message: Copy the doc for GetFaceElementTransformations from mesh to pmesh.
diff: @@ -357,6 +357,36 @@ public:
  with indices offset by the local number of elements. */
  Table *GetFaceToAllElementTable() const;
  + /// Returns (a pointer to an object containing) the following data:
  + ///
  + /// 1) Elem1No - the index of the first element that contains this face this
  + /// is the element that has the same outward unit normal vector as the
  + /// face;
  + ///
  + /// 2) Elem2No - the index of the second element that contains this face this
  + /// element has outward unit normal vector as the face multiplied with -1;
  + ///
  + /// 3) Elem1, Elem2 - pointers to the ElementTransformation's of the first
  + /// and the second element respectively;
  + ///
  + /// 4) Face - pointer to the ElementTransformation of the face;
  + ///
  + /// 5) Loc1, Loc2 - IntegrationPointTransformation's mapping the face
  + /// coordinate system to the element coordinate system (both in their
  + /// reference elements). Used to transform IntegrationPoints from face to
  + /// element. More formally, let:
  + /// TL1, TL2 be the transformations represented by Loc1, Loc2,
  + /// TE1, TE2 - the transformations represented by Elem1, Elem2,
  + /// TF - the transformation represented by Face, then
  + /// TF(x) = TE1(TL1(x)) = TE2(TL2(x)) for all x in the reference face.
  + ///
  + /// 6) FaceGeom - the base geometry for the face.
  + ///
  + /// The mask specifies which fields in the structure to return:
  + /// mask & 1 - Elem1, mask & 2 - Elem2
  + /// mask & 4 - Loc1, mask & 8 - Loc2, mask & 16 - Face.
  + /// These mask values are defined in the ConfigMasks enum type as part of the
  + /// FaceElementTransformations class in fem/eltrans.hpp.
  FaceElementTransformations *GetFaceElementTransformations(
  int FaceNo,
  int mask = 31) override;
  