$KEYCHK(keycode list) 
Restrictions: Match only
Filter Types: All

The KEYCHK command can be used to test for user keypress combinations
during a filter test (for example, to have a filter bypass itself or
act differently if the user is pressing a specific key). It works like
any matching test and can be used in a filter's match or a URL match.
When the match is done KEYCHK will return as "matched" if the keys
being tested for are currently pressed. Most keys can be tested by
using their *unshifted* values. However, there's several special key
tests which begin with a carat "^" symbol....

^C = CONTROL
^A = ALT
^S = SHIFT
^T = TAB
^F1 = Function key #1
^F2 = Function key #2
^32 = Virtual keycode 32 (spacebar)
^65 = Virtual keycode 65 ("A")

Characters are not case sensitive so either "^c" or "^C" may be used.
Multiple keys can be included to test for combinations. For example... 

$KEYCHK(^A^S) = ALT+SHIFT
$KEYCHK(^C^F6) = CONTROL+F6
$KEYCHK(^AG) = ALT+G
$KEYCHK(^C^A^S) = CONTROL+ALT+SHIFT

This will work for any combination the keyboard allows. Other special
keys can also be tested if you know the Windows virtual keycode - this
is a number between 0-255. For instance ^2 tests for the right mouse
button.

=======================================================================

Virtual Key Codes

1        Left mouse button
2        Right mouse button
3        Control+Break
4        Middle mouse button
8        Backspace key
9        Tab key
12       Clear key
13       Enter key
16       Shift key
17       Ctrl key
18       Alt key
19       Pause key
20       Caps Lock key
27       Esc key
32       Spacebar
33       Page Up key
34       Page Down key
35       End key
36       Home key
37       Left arrow key
38       Up arrow key
39       Right arrow key
40       Down arrow key
41       Select key
43       Execute key
44       Print Screen key
45       Insert key
46       Delete key
47       Help key
48-57    0 through 9, respectively
65-90    A through Z, respectively
91       Left Windows key  (104-key keyboard)
92       Right Windows key (104-key keyboard)
93       Application key   (104-key keyboard)
96-105   Numeric keypad 0 thru 9, respectively
106      Multiply key
107      Add key
108      Separator key
109      Subtract key
110      Decimal key
111      Divide key
112-135  F1 through F24, respectively
144      Num Lock key
145      Scroll Lock key

Undefined: 5-7, 10, 11, 14, 15, 26, 58-64, 94-95.
Reserved for Kanji systems: 21-25, 28-31.
Unassigned: 136-143, 146-185, 193-218, 229, 231, 232, 246-255.
OEM specific: 42, 186-192, 219-228, 230, 233-245.

=======================================================================