Asp.NET Filtered TextBox Extender - Invalid Char Sequence?

Is it possible to put a character sequence in a Filtered TextBox Extender in Asp.NET? My guess is no, but I'm curious. I want the user to be able to enter the characters (such as & and #), but not enter the invalid sequences (such as &#).

Why not just use a regular expression? Because when the form is submitted, all the fields are passed to the server...including fields that are not part of the validation group. These fields do not get checked and may trigger the开发者_Go百科 "A potentially dangerous Request.Form value…”, aka the HttpRequestValidationException. And preventing that message is the whole point of this. I'd rather tell the user, with a regex validator, what they are doing wrong...but I will settle for preventing them from typing the bad chars (&#, <, >).

Edit: sort of an afterthought, but if there's a better way to prevent ALL TextBoxes from including the characters, that'd be great!

You can just have a function onkeydown for all your text boxes and that checks the character pressed and if it's invalid just remove that last character. Also for your combination strings you can just check to see if the previous characters make it invalid then remove all of them.

An example of that type of function is:

function checkKey(event) {
 var code = event.keyCode;
 // code is the ascii number of the key.
}