 TUPLE: interpolated var ;
 C: <interpolated> interpolated
 
-UNION: nullable-string string POSTPONE: f ;
-
 TUPLE: name
-    { space nullable-string }
+    { space maybe{ string } }
     { main string }
-    { url nullable-string } ;
+    { url maybe{ string } } ;
 C: <name> name
 
 : ?= ( object/f object/f -- ? )

    { att-defs string } ;
C: <attlist-decl> attlist-decl

UNION: boolean t POSTPONE: f ;

TUPLE: entity-decl < directive
    { name string }
    { def string }


TUPLE: public-id { pubid-literal string } { system-literal string } ;
C: <public-id> public-id

TUPLE: dtd
    { directives sequence }
