Add a comment for a recent patch.

source/grid/grid_reordering.cc

@@ -32,17 +32,23 @@ DEAL_II_NAMESPACE_OPEN
 namespace
 {
   /**
-   * A set of functions that
-   * reorder the data from the
-   * "current" to the "classic"
-   * format of vertex numbering of
-   * cells and faces. These functions
-   * do the reordering of their
-   * arguments in-place.
+   * This file uses a different ordering for the vertices in a hex
+   * cell than we usually do in deal.II. The different convention used
+   * here originates in what we believed the ordering to be in UCD
+   * format, until it was discovered in 2022 that UCD will interpret
+   * this ordering to correspond to inverted cells -- as a
+   * consequence, the UCD ordering was fixed, but the current file is
+   * stuck on the old ordering.
    */
   constexpr std::array<unsigned int, 8> local_vertex_numbering{
     {0, 1, 5, 4, 2, 3, 7, 6}};
 
+  /**
+   * Following is a set of functions that reorder the data from the
+   * "current" to the "classic" format of vertex numbering of cells
+   * and faces. These functions do the reordering of their arguments
+   * in-place.
+   */
   void
   reorder_new_to_old_style(std::vector<CellData<1>> &)
   {}