Tandy 600 Owner's Manual page 112

Special keys for the command fields are:
ITABI
t
SHIFT II TAB
t
space bar
I
BKSP
I
Moves to the next command field.
Moves to the previous command field.
Moves to the next item in a menu-type command
field.
Moves to the previous item in a menu-type
command field.
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