0021815: EDF 2347 SMESH : Error when meshing vertices

Update documentation: add explanation about meaning of "3D", "2D", "1D" and "0D" pages in "Create mesh" dialog box.

doc/salome/gui/SMESH/input/constructing_meshes.doc

@@ -34,6 +34,27 @@ written in Python.
     \subpage about_hypo_page "hypotheses" which will be used at computation of
     this mesh.
 
+    "Create mesh" dialog box contains several tab pages titled \b 3D,
+    \b 2D, \b 1D and \b 0D. The title of each page reflects the
+    dimension of the CAD model (geometry) the algorithms listed on
+    this page affect to. For example, \b 3D page lists algorithms
+    that affect 3D geometrical objects (solids).
+
+    \note
+    - Some page(s) can be disabled - if the source geometrical
+    object does not include shapes (sub-shapes) of the corresponding
+    dimension(s). For example, if input object is a geometrical face,
+    \b 3D page is disabled.
+    - Some algorithms affect on geometry of several dimensions,
+    i.e. "1D-2D" or "1D-2D-3D". If such algorithm is selected by the
+    user, dialog box pages related to the corresponding lower level
+    dimensions are disabled.
+    - \b 0D page does not refer to the 0D elements, but to 0D
+    geometry (vertices). Mesh module does not provide algorithms that
+    produce 0D elements. Currently \b 0D page provides only one
+    algorithm "Segments around vertex" that allows specyfing required
+    size of mesh edges about some selected vertex(vertices).
+
     For example, you need to mesh a 3D object.
 
     First, type the name for your mesh in the \b Name box, by default,