Add a text attribute to your site that includes advanced validation (e.g. URL, email address), including RegExp. Also, formatting of the output value.
This package could be so much more; contribute to it on Github.
This is a replacement for the existing c5 text attribute. It behaves the same, but allows you, during setup (ie, the place where you define the handle), to add validation and formatting options. The following are the existing validation options:
Additionally, you can choose that, when not being edited, the value is formatted. For example, if it's validated as a URL it'll be displayed as a clickable URL.