In step-10, fixes explanation surrounding new header inclusion. fixes 9356

diff --git a/examples/step-10/step-10.cc b/examples/step-10/step-10.cc
index 36662569b30b79c334e266faf43040c5c537a3d6..4ee00fdebd901bb2fea5e0d20fdd9e53fad1df2a 100644 (file)
--- a/examples/step-10/step-10.cc
+++ b/examples/step-10/step-10.cc
@@ -30,10 +30,14 @@
 #include <deal.II/grid/grid_out.h>
 #include <deal.II/dofs/dof_handler.h>
 #include <deal.II/dofs/dof_accessor.h>
-#include <deal.II/fe/fe_nothing.h>
 #include <deal.II/fe/fe_values.h>
 
-// This is the only new one: in it, we declare the MappingQ class
+// This include file is new. Even if we are not solving a PDE in this tutorial,
+// we want to use a dummy finite element with zero degrees of freedoms provided
+// by the FE_Nothing class.
+#include <deal.II/fe/fe_nothing.h>
+
+// The following header file is also new: in it, we declare the MappingQ class
 // which we will use for polynomial mappings of arbitrary order:
 #include <deal.II/fe/mapping_q.h>