better explanation of Boundary

doc/texinfo/gmsh.texi

@@ -2366,23 +2366,17 @@ Translates all elementary entities in @var{transform-list}. The
 the X, Y and Z components of the translation vector.
 
 @item Boundary @{ @var{transform-list} @}
-(Not a transformation per-se.) Returns the boundary of the elementary
-entities in @var{transform-list}. 
+(Not a transformation per-se.) Returns the entities on the boundary of
+the elementary entities in @var{transform-list}, with signs indicating
+their orientation in the boundary. To get unsigned tags (e.g. to reuse
+the output in other commands), apply the @code{Abs} function on the
+returned list.
 
 @item CombinedBoundary @{ @var{transform-list} @}
 (Not a transformation per-se.) Returns the boundary of the elementary
 entities, combined as if a single entity, in
 @var{transform-list}. Useful to compute the boundary of a complex part.
 
-@item OrientedBoundary @{ @var{transform-list} @}
-(Not a transformation per-se.) Returns the boundary of the elementary
-entities in @var{transform-list}, with signs indicating their orientation.
-
-@item CombinedOrientedBoundary @{ @var{transform-list} @}
-(Not a transformation per-se.) Returns the (oriented) boundary of the
-elementary entities, combined as if a single entity, in
-@var{transform-list}. Useful to compute the boundary of a complex part.
-
 @c @item Intersect Line @{ @var{expression-list} @} Surface @{ @var{expression} @}
 @c (Not a transformation per-se.) Returns the intersections of the lines
 @c given in @var{expression-list} with the specified surface.