I'm looking for a module that will let me limit users to certain domain names when they edit a Link field.

For example, only let users enter a URL if the domain name is `facebook.com`, `twitter.com` or `plus.google.com`.

This list must be easily editable by admins.

Does such a module exist?

(Also: See my [other question](http://drupal.stackexchange.com/questions/22410/module-to-display-a-websites-favicon-when-displaying-a-link-to-it), if there is some a module that can do both it'll be great)