That was referring to the "Accept only letters in a field" post in the "Post a javascript" forum.
And ahosang is right - allow is a variable that Borgtex defined in the script. Since you asked how it works, here's a breakdown:
<head>
<script type="text/javascript">
<!--
var letters=' ABCÇDEFGHIJKLMNÑOPQRSTUVWXYZabcçdefghijklmnñopqrstuvwxyzàáÀÁéèÈÉíìÍÌïÏóòÓÒúùÚÙüÜ'
var numbers='1234567890'
var signs=',.:;@-''
var mathsigns='+-=()*/'
var custom='<>#$%&?¿'
function alpha(e,allow) { // allow is declared here! Its value depends on what is passed to the function (see the HTML below).
var k;
k=document.all?parseInt(e.keyCode): parseInt(e.which); // this gets the key that was pressed on the keyboard!
return (allow.indexOf(String.fromCharCode(k))!=-1); // this returns a boolean (true or false) of whether the key pressed on the keyboard is in the var(s) above that correspond to allow!
}
// -->
</script>
</head>
<body>
<div>
<form id="example" action="java script://">
<input type="text" onkeypress="return alpha(event,numbers)" /> <!-- "event" is a javascript handler, which gets passed to "e" in the function "alpha()". The stuff after "event," is what gets passed to "allow" -->
<input type="text" onkeypress="return alpha(event,letters)" /> <!-- "event" is a javascript handler, which gets passed to "e" in the function "alpha()". The stuff after "event," is what gets passed to "allow" -->
<input type="text" onkeypress="return alpha(event,numbers+letters+signs)" /> <!-- "event" is a javascript handler, which gets passed to "e" in the function "alpha()". The stuff after "event," is what gets passed to "allow" -->
</form>
</div>
</body>
</html>
Get it?
A simpler example:
<script type="text/javascript">
<!--
function test(mystring){
alert(mystring);
}
test("Yay!");
// -->
</script>
P.S. The action="javascript://" in the <form> tag basically does absolutely nothing - it's just in there as a placeholder since the "action" attribute of a form tag is required in XHTML.
:D