Straight from Access Help:
(Input Mask / Create an input mask to control how data is
entered in a field or control)
0 Digit (0 through 9, entry required;
plus [+] and minus [-] signs not allowed).
9 Digit or space (entry not required;
plus and minus signs not allowed).
# Digit or space (entry not required;
blank positions converted to spaces,
plus and minus signs allowed).
L Letter (A through Z, entry required).
? Letter (A through Z, entry optional).
A Letter or digit (entry required).
a Letter or digit (entry optional).
& Any character or a space (entry required).
C Any character or a space (entry optional).
.. , : ; - / Decimal placeholder and thousands,
date, and time separators.
(The actual character used depends
on the regional settings specified
by double-clicking Regional Settings
in the Windows Control Panel.)
< Causes all characters that follow to be converted
to lowercase.
Causes all characters that follow to be converted
to uppercase.
! Causes the input mask to display from right to left,
rather than from left to right. Characters typed into
the mask always fill it from left to right. You can
include the exclamation point anywhere in the input
mask.
\ Causes the character that follows to be displayed
as a literal character. Used to display any of the
characters listed in this table as literal characters
(for example, \A is displayed as just A).
Password Setting the InputMask property to the word
Password creates a password entry text box.
Any character typed in the text box is stored
as the character but is displayed as
an asterisk (*).
