WML » input » format

The optional format attribute specifies which input mask is in effect. An input mask dictates which alphanumeric and punctuation characters can be entered by the user and the order in which they must occur. The default is equivalent to *M (any number of any characters, but all characters are treated as uppercase for date entry).
 
The permitted values are:

ValueDescription
A Any uppercase alphabetic or punctuation character
a Any lowercase alphabetic or punctuation character
N Any numeric character
* N Any number of any numeric characters
X Any uppercase character>
x Any lowercase character
M> Any character, but is treated as uppercase for date entry
*M Any number of any characters, but is treated as uppercase for date entry
m Any character, but is treated as lowercase for data entry
* f Any number of any type of characters
n f Any n integer number of any characters
\c Display the character after the slash in the display

Note that you can add an asterisk as a prefix to indicate multiple characters (i.e., *X)
or add an integer as a prefix to set a fixed number of characters (i.e., 5X).