src/Pure/Isar/parse.scala

     def name: Parser[String] = atom("name declaration", _.is_name)
     def xname: Parser[String] = atom("name reference", _.is_xname)
     def text: Parser[String] = atom("text", _.is_text)
     def ML_source: Parser[String] = atom("ML source", _.is_text)
     def doc_source: Parser[String] = atom("document source", _.is_text)
-    def path: Parser[String] = atom("file name/path specification", _.is_name)
+    def path: Parser[String] =
+      atom("file name/path specification", tok => tok.is_name && Path.is_ok(tok.content))
+    def theory_name: Parser[String] =
+      atom("theory name", tok => tok.is_name && Thy_Load.is_ok(tok.content))
 
     private def tag_name: Parser[String] =
       atom("tag name", tok =>
           tok.kind == Token.Kind.IDENT ||
           tok.kind == Token.Kind.STRING)