enhanced documentation for DoFTools::Coupling::nonzero

diff --git a/include/deal.II/dofs/dof_tools.h b/include/deal.II/dofs/dof_tools.h
index 379cdc5f182190c3d636d80d743b34bc8d258869..2dd019639dd29b80d9ba795cf4c22bd9df2f625b 100644 (file)
--- a/include/deal.II/dofs/dof_tools.h
+++ b/include/deal.II/dofs/dof_tools.h
@@ -214,6 +214,8 @@ namespace DoFTools
      * Two components couple only if their shape functions are both nonzero on
      * a given face. This flag is only used when computing integrals over
      * faces of cells, e.g., in DoFTools::make_flux_sparsity_pattern().
+     * Use Coupling::always in general cases where gradients etc. occur on face
+     * integrals.
      */
     nonzero
   };