CFSimpleIndexer.md

@@ -139,6 +139,13 @@ Finally, the values of `hpg::VisData<N>::m_cf_index` may be computed as in the f
 ```c++
   hpg::VisData<N> vis;
   // initialize fields of cell_index using visibility metadata
+  //
+  // Note that in this example, we're implicitly relying on the
+  // inverse of w_map. The mueller_map is irrelevant here, as
+  // for present purposes, we're not interested in the mueller
+  // value returned by the call to CFSimpleIndexer::cf_index(),
+  // and so just provide a universally valid value (0) to the 
+  // CellIndex constructor.
   hpg::CellIndex cell_index(
     0,       // baseline type
     /*...*/, // time