Tandy 600 Programmer's Reference Manual page 134

70h
Keyboard
Queue
Hook,
for
European key
layout
(Initialized
as IRET)
This
hook can be invoked
right
before invocation
of
"INT
4FH
—
Keyboard
Queue
Hook."
Key
layout
can be modified
for
European key
layouts
by
using
this
hook.
71
h
BIOS
Special
Extended
Function Support. This support
is
provided
for
installable printer drivers.
129