src/Pure/PIDE/resources.scala

     val reader = Scan.byte_reader(path.file)
     try { f(reader) } finally { reader.close }
   }
 
   def check_thy_reader(qualifier: String, node_name: Document.Node.Name,
-    reader: Reader[Char], start: Token.Pos): Document.Node.Header =
+    reader: Reader[Char], start: Token.Pos = Token.Pos.command): Document.Node.Header =
   {
     if (reader.source.length > 0) {
       try {
         val header = Thy_Header.read(reader, start).decode_symbols
 

       catch { case exn: Throwable => Document.Node.bad_header(Exn.message(exn)) }
     }
     else Document.Node.no_header
   }
 
-  def check_thy(qualifier: String, name: Document.Node.Name, start: Token.Pos)
+  def check_thy(qualifier: String, name: Document.Node.Name, start: Token.Pos = Token.Pos.command)
     : Document.Node.Header =
     with_thy_reader(name, check_thy_reader(qualifier, name, _, start))
 
   def check_file(file: String): Boolean =
     try {