See demo screencast at: http://bit.ly/dqZeB3
This is a simple package which highlights textstring inputs in Umbraco when their value doesn't match the validation regular expression.
This prevents the user from having to hit save to find out whether their entry is valid.
Highlighting is applied and removed on each keystroke.
Due to restrictions in how Umbraco works the validator is supplied as a 'dummy' datatype which must be added to the content type where you wish to use the validator.
For a full demonstration please view the screencast.