src/Pure/General/symbol.scala

   def is_symbolic_char(sym: Symbol): Boolean = symbols.sym_chars.contains(sym)
 
 
   /* control symbols */
 
+  val control_prefix = "\\<^"
+  val control_suffix = ">"
+
+  def is_control_encoded(sym: Symbol): Boolean =
+    sym.startsWith(control_prefix) && sym.endsWith(control_suffix)
+
   def is_control(sym: Symbol): Boolean =
-    (sym.startsWith("\\<^") && sym.endsWith(">")) || symbols.control_decoded.contains(sym)
+    is_control_encoded(sym) || symbols.control_decoded.contains(sym)
 
   def is_controllable(sym: Symbol): Boolean =
     !is_blank(sym) && !is_control(sym) && !is_open(sym) && !is_close(sym) &&
     !is_malformed(sym) && sym != "\""