Regex that allow numbers,question mark and asteriks

There is several key event that can be handled for user input controlling.

for simplification I will only talk about onkeypress

to process a user input you must have to return true or false.

as example

<input type=text onkeypress='return false;'> <!-- this will discard whatever the user types-->
<input type=text onkeypress='return false;'> <!-- this will allow whatever the user types-->

try this on browser.

say you want to allow only 0 and 1. the simple example would be

<script>
function test(e){
 var e=window.event || e
 //alert(e.charCode);
 return e.charCode==48 || e.charCode==49 ? true:false;
}
</script>

<input type=text onkeypress='return test(event);'> <!--only let you print 0 or 1 -->

hope it will guide you a little