diff --git a/doc/salome/gui/SMESH/input/projection_algos.doc b/doc/salome/gui/SMESH/input/projection_algos.doc
index 07e7c343e..5f4508147 100644
--- a/doc/salome/gui/SMESH/input/projection_algos.doc
+++ b/doc/salome/gui/SMESH/input/projection_algos.doc
@@ -23,9 +23,12 @@ It could also be necessary to define the orientation of edges,
 which is done by indicating the <b>Source Vertex</b> being the first point 
 of the Source Edge and the <b>Target Vertex</b> being the first point of 
 the created \b Edge. 
+<br>
 For a group of edges, <b>Source</b> and <b>Target</b> vertices should be
-shared by only one edge of the group. If <b>Source</b> and
-<b>Target</b> vertices are specified, the elements of the group must be ajacent.
+shared by one edge of the group. If <b>Source</b> and <b>Target</b>
+vertices are specified, the elements of the group must be ajacent.
+The source and target groups must contain equal number of edges
+and they must form topologically equal structures.
 
 \n <b>Projection 2D</b> algorithm allows to define the mesh of a face
 (or group of faces) by the
@@ -45,10 +48,12 @@ following dialog box will appear:
 In this menu you can define the \b Name of the algorithm, the already
 meshed source \b Face and the \b Mesh (It can be omitted only when 
 projecting a submesh on another one from the same global Mesh). 
-It could also be necessary to define the orientation of mesh on the face
-, which is done by indicating two <b>Source Vertices</b>, which belong 
-to the same edge of the source face, and two <b>Target Vertices</b>, which 
-belong to the same edge of the created \b Face.
+It could also be necessary to define the orientation of mesh on the
+face, which is done by indicating two <b>Source Vertices</b>, which
+belong to the same edge of the source face, and two <b>Target
+Vertices</b>, which belong to the same edge of the created \b Face.
+For groups of face, they must contain equal number of faces
+and they must form topologically equal structures.
 
 \n <b>Projection 3D</b> algorithm allows to define the mesh of a shape by
 the projection of another already meshed shape.  This algorithm works