Making custom extendedUserData fields required

Is it possible to make or mark an extendedUserData field required?

From David Rhodes

Use the RequiredFieldValidator ASP.NET control.

With regards to validators and ExtendedUserData, I ran into an issue when
building The Hive. We needed users to agree to an additional "Terms of
Service" type document before allowing them to submit their registration.
Since ASP.NET doesn't come with a requiredfieldvalidator that works with
checkboxes (kinda makes sense), I added one to the CommunityServer.Controls
project in v2.0 (and it's still around in v2.1).

So, if you need to guarantee that a checkbox is checked be sure to use the
RequiredCheckBoxValidator. You can see the code here.

Thanks.