doc-src/IsarRef/syntax.tex

 identifiers are excluded).  Quoted strings provide an escape for
 non-identifier names or those ruled out by outer syntax keywords (e.g.\ 
 \verb|"let"|).  Already existing objects are usually referenced by
 \railqtoken{nameref}.
 
-\indexoutertoken{name}\indexoutertoken{nameref}
+\indexoutertoken{name}\indexoutertoken{parname}\indexoutertoken{nameref}
 \begin{rail}
   name : ident | symident | string
+  ;
+  parname : '(' name ')'
   ;
   nameref : name | longident
   ;
 \end{rail}