Comment stuff in the new solver

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -28,7 +28,8 @@ pub(crate) fn deeply_normalize<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
 /// its input to be already fully resolved.
 ///
 /// Additionally takes a list of universes which represents the binders which have been
-/// entered before passing `value` to the function.
+/// entered before passing `value` to the function. This is currently needed for
+/// `normalize_erasing_regions`, which skips binders as it walks through a type.
 pub(crate) fn deeply_normalize_with_skipped_universes<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     at: At<'_, 'tcx>,
     value: T,