In CommunityConfiguration we used an internal "MediaWiki page title" defintion which uses the page title control targeting pages in the same wiki. No URL validation happens since the page is stored using its title (DB key) in plain text, eg: Main_Page. I think this may be enough for an mvp but maybe we want to support external links as well in the future which would benefit from some URL validation. Can we confirm we are only targeting wiki pages on this task? cc @KStoller-WMF

Given that we've already received community feedback that organizers often want to link to an external page, we might want to allow any URL and remove the URL validation for the initial experiment.

I'm not sure we should allow any external link, as it would create a way out of the wiki without that being really obvious, which is a type of issue Legal is interested in, and we would need to coordinate with them before going ahead.

Limiting to internal link targets (so local links or interwiki links) would cover needs like metawiki or commonswiki (or even some chapter wikis), but it would drastically reduce the amount of things that might be linked. FWIW, this would restrict the linkable stuff to Wikimedia wikis plus approved sites listed at https://meta.wikimedia.org/wiki/Interwiki_map (managed by Stewards and Meta-Wiki admins).

That sounds like a good compromise for now, and hopefully covers most community use cases. I've adjusted the task description.