The <input> tag

<input name="somename"/>

A = uppercase alphabetic or punctuation characters
a  = lowercase alphabetic or punctuation characters
N = numeric characters
X = uppercase characters
x  = lowercase characters
M = all characters
m  = all characters
*f = Any number of characters. Replace the f with one of the letters above to specify what characters the user can enter
nf  = Replace the n with a number from 1 to 9 to specify the number of characters the user can enter. Replace the f with one of the letters above to specify what characters the user can enter

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>
<card title="Input">
<p> 
 Name: <input name="name" size="15"/><br/> 
 Age:  <input name="age" size="15" format="*N"/><br/>
 Sex:  <input name="sex" size="15"/>
</p>
</card> 
</wml>