Last modified: 2010-06-19 16:22:05 UTC
At the moment it is impossible to pre-validate a euprotocol about to be supplied to the API on a wiki because $wgUrlProtocols itself (from which I gather euprotocol inherits its acceptable values) is completely unaccessible via the API. They should be accessible via siteinfo or similar in order to allow this.
http://en.wikipedia.org/w/api.php?action=paraminfo&querymodules=exturlusage