Problem of CTL
 
  CTL requires knowledge specific to script.
      It is almost impossible to have a single CTL program, and drive it with different parameters for different scripts.
      We need different codes for different scripts.
  Need updating fairly often
      Unicode adds new scripts.
      Unicode adds new characters to existing scripts.
      Unicode adds new layouting rules.
  When represented in hard-coded C program...
      difficult to undrestand
      difficult to maintain
  Currently different application uses different CTL code.
      Gtk/Pango, Qt, OpenOffice/ICU
      Fixing one doesn't mean fixing the others.