All output for the SAY/GET system is character based. There are two
major vectors in the SAY/GET system allowing a programmer to establish their
own output drivers.

        The first is the dword [ __$SG_OUTPUT ]. This dword points to a routine
responsible for the output of a character to the screen. At the time of the
call to [ __$SG_OUTPUT ], the registers are set as follows:

           AL = character to output
        ES:DI = points to location on screen

Only AL and DI may be modified by your output routine.

All template and "function" formatting has been accomplished when the call to 
[ __$SG_OUTPUT ] is made.

        The second pointer is [ __$READ_PROC ]. This vector is used when the
READ command is called. Use this vector to establish an environment important
to the READ that is global, i.e., initializing a cursor system.

        To use [ __$READ_PROC ], set the vector to your own routine. When your
new routine has accomplished its tasks, then call _$READ_DWORD. (_$READ_DWORD
is a FAR procedure). _$READ_DWORD will return to you when the GETs are
finished. Just issue a far return to leave your vector routine.

        To "deinstall" your [ __$READ_PROC ] routine, set the dword [
__$READ_PROC ] to -1.