tcl3270 emulates one of four models of an IBM 3278 or 3279 terminal. The difference between the various models is the screen size. The emulation is not quite complete; tcl3270 understands extended field orders but does not implement some of the extended attributes (outlining, extended validation, etc.). It does not support 3179G bit-mapped graphics (GDDM).
tcl3270 supports the APL character set and several international character sets. Many APL and international symbols may be entered by their X11 symbol names.