The GL and GR keywords take one of the following keyword values:

     G0, G1, G2, G3.           E.g. CHARACTER_SET=(GL=G0,GR=G2).

  GL=G0 outputs "<SI>".
  GL=G1 outputs "<SO>".
  GL=G2 outputs "<ESC>n".
  GL=G3 outputs "<ESC>o".