(Just x, Just y) -> mkPageFragmentURI baseURI x y
(Just x, Nothing) -> mkPageURI baseURI x
(Nothing, Just y) -> mkFragmentURI y
(Just x, Just y) -> mkPageFragmentURI baseURI x y
(Just x, Nothing) -> mkPageURI baseURI x
(Nothing, Just y) -> mkFragmentURI y