+let string_of_entry = function
+ | `About `Blank -> "about:blank"
+ | `About `Current_proof -> "about:proof"
+ | `About `Us -> "about:us"
+ | `Check _ -> "check:"
+ | `Cic (_, _) -> "term:"
+ | `Dir uri | `Uri uri -> uri
+ | `Whelp (query, _) -> query
+