category Extend.X for unclassified words, as in UD

src/abstract/Extend.gf

@@ -287,4 +287,6 @@ fun UseDAP     : DAP -> NP ;
     UseDAPMasc : DAP -> NP ;
     UseDAPFem  : DAP -> NP ;
 
+cat X ; -- for words that are difficult to classify, mainly for MorphoDict
+
 }

src/common/ExtendFunctor.gf

@@ -4,6 +4,8 @@ lincat
   RNP = Grammar.NP ;
   RNPList = Grammar.ListNP ;
 
+  X = {s : Str} ; -- for words that are difficult to classify, mainly for MorphoDict
+
 lin
   BaseVPS = variants {} ;
   ConsVPS = variants {} ;