src/Pure/General/yxml.ML

   X Y X
 *)
 
 signature YXML =
 sig
+  val X: Symbol.symbol
+  val Y: Symbol.symbol
   val embed_controls: string -> string
   val detect: string -> bool
   val output_markup: Markup.T -> string * string
   val element: string -> XML.attributes -> string list -> string
   val string_of_body: XML.body -> string

   else str;
 
 
 (* markers *)
 
-val X = Symbol.ENQ;
-val Y = Symbol.ACK;
+val X = chr 5;
+val Y = chr 6;
 val XY = X ^ Y;
 val XYX = XY ^ X;
 
 val detect = exists_string (fn s => s = X);