Hopefully these behaviours will converge in future releases.
~ characters are legal in the local part of an e-mail address but in the above regular expression those characters are filtered out. It begins with at least one or more word characters including the underscore, equivalent to [A-Za-z0-9_].
Now you can ask questions directly to me on my new site ASPForums.
As mentioned above, we can improve on this by making use of the are already implicit so the input has to match the entire expression. If anyone wants to contribute a more thorough expression to test for valid email or url format, feel free to post it using the Feedback option above.. Since it is not possible to recurse when using a regular expression it is also not possible to create a truly accurate regex for doing email address validation.
The value, clicking 'down' with the input blank will result in a very large number. The examples posted in these responses are vastly oversimplified when compared against reality.
The simplest change you can make to your forms is to mark a text input field as 'required': This informs the (HTML5-aware) web browser that the field is to be considered mandatory.