Introduce numbers::invalid_boundary_id. Fix up documentation in a couple of other...

git-svn-id: https://svn.dealii.org/trunk@27682 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/include/deal.II/base/types.h b/deal.II/include/deal.II/base/types.h
index e6358656402e2959c9031a95cb4673d470b36346..87b2d5531d381d4b7ecf9e23ba95c75b5b5f43e2 100644 (file)
--- a/deal.II/include/deal.II/base/types.h
+++ b/deal.II/include/deal.II/base/types.h
@@ -136,11 +136,25 @@ namespace numbers
   const types::material_id invalid_material_id = static_cast<types::material_id>(-1);
 
   /**
-   * The number which we reserve for
+   * Invalid boundary_id which we
+   * need in several places as a
+   * default value.  We assume that
+   * all valid boundary_ids lie in the
+   * range [0, invalid_boundary_id).
+   */
+  const types::boundary_id invalid_boundary_id = static_cast<types::boundary_id>(-1);
+
+  /**
+   * A boundary indicator number that we reserve for
    * internal faces.  We assume that
-   * all boundary_ids lie in the
+   * all valid boundary_ids lie in the
    * range [0,
    * internal_face_boundary_id).
+   *
+   * This is an indicator that is used internally (by the library) to
+   * differentiate between faces that lie at the boundary of the domain
+   * and faces that lie in the interior of the domain. You should never try
+   * to assign this boundary indicator to anything in user code.
    */
   const types::boundary_id internal_face_boundary_id = static_cast<types::boundary_id>(-1);