Canon Cat Reference Manual page 14

ILOCKI
is
nrmed
off
by
pressing and releasing either
[SHIFT].
When ILoCK] is released the
light in
the
keycap
goes
off.
[LocK]
and its keycap
light
temporarily swirch off during
leaping.
Since leaping
is
sensitive
to capital letters
in
patt€rns, [LOCK]
would
make
leaping appear to be out
of
order
if it
were
left
on during the
leap. When
you
release
the
LEAP key, [LOCK] is turned on again.
The Cat also
ignores
[LOCK]
while you press
[USE
FRONT].
This
is
because
certain commands behave
differently
when [SHIFT]
is pressed, and using
[LOCK]
is
like holding
down
[SHIFT].