-/// primary namespaces and sub-namespaces (`""`) are assumed to be a valid, however, if
-/// `primary_namespace` is empty, `sub_namespace` is required to be empty, too. This means that
-/// concerns should always be separated by primary namespace first, before sub-namespaces are used.
-/// While the number of primary namespaces will be relatively small and is determined at compile
-/// time, there may be many sub-namespaces per primary namespace. Note that per-namespace
-/// uniqueness needs to also hold for keys *and* namespaces in any given namespace, i.e., conflicts
-/// between keys and equally named primary-namespaces/sub-namespaces must be avoided.
+/// primary namespaces and secondary namespaces (`""`) are assumed to be a valid, however, if
+/// `primary_namespace` is empty, `secondary_namespace` is required to be empty, too. This means
+/// that concerns should always be separated by primary namespace first, before secondary
+/// namespaces are used. While the number of primary namespaces will be relatively small and is
+/// determined at compile time, there may be many secondary namespaces per primary namespace. Note
+/// that per-namespace uniqueness needs to also hold for keys *and* namespaces in any given
+/// namespace, i.e., conflicts between keys and equally named
+/// primary namespaces/secondary namespaces must be avoided.