HDF5: Improve a comment

dune/fufem/hdf5/file.hh

@@ -38,14 +38,14 @@ public:
       : readOnly_(access == Access::READONLY) {
     struct stat buffer;
 
-    /* Use the latest HDF5 format.
-       Upside  : We can use new features like SWMR.
-       Downside: Tools that make use of old HDF5 versions cannot read
-                 the output. This should not be a problem in practice
-                 since h5repack can be used to restore compatibility
-                 with older versions if needed. */
+    /* Use the latest HDF5 format (as opposed to: the latest format that supports
+                                   the set of features we use: H5F_LIBVER_EARLIEST)
+       Upside  : Improvements in speed, file size
+       Downside: Output cannot be read by old tools/libraries
+       Remedy:   h5repack and h5format_convert can restore compatibility. */
+    H5F_libver_t const minimumVersion = H5F_LIBVER_LATEST;
     hid_t fapl = H5Pcreate(H5P_FILE_ACCESS);
-    H5Pset_libver_bounds(fapl, H5F_LIBVER_LATEST, H5F_LIBVER_LATEST);
+    H5Pset_libver_bounds(fapl, minimumVersion, H5F_LIBVER_LATEST);
 
     bool const fileExists = stat(filename.c_str(), &buffer) == 0;
     bool const createFile = !fileExists;