all: assorted cleanups

src/util/xspan_impl_common.h

@@ -280,6 +280,7 @@ public:
             return Self(Unchecked, end, (begin - end) * sizeof(T), end);
     }
 
+    // cast to a different type (creates a new value)
     template <class U>
     inline CSelf<U> type_cast() const {
         typedef CSelf<U> R;