Regular Expression for Restricting Characters

If you are getting the value from the user on a text box/area or something and you don't want user to allow user to enter some characters like html tags(<,>,* etc).

Then it is better to use regular expression which will cause Page Invalid .

For that steps are…

1. Add one Textbox/area and one RegularExpressionValidator.
   
2. Set properties for RegularExpressionValidator.
   
3. In ValidationExpression property set value "[^<>/?&{};#]+".
   

Just Over. This will not allow user to enter the symbols given above. (< , > , / , ? , & , { , } , ; , # ).

You can add or remove other text/symbols/numbers to the above list.

If you want to allow user to enter the characters from certain range then    

1. In ValidationExpression property set value "^[a-zA-Z]*$".
   

This will allow user to enter only the characters from a to z and A to Z.

1. In ValidationExpression property set value "^[a-zA-Z0-9]*$" .
   

This will allow user to enter only the characters from a to z and A to Z and also 0 to 9.

1. In ValidationExpression property set value "^[a-zA-Z .]*$" .
   

This will allow user to enter only the characters from a to z and A to Z Space and Dot. (Ex Mr. Xyz Mno)