https://doc.wikimedia.org/ RESTBase link goes to https://rest.wikimedia.org/, which is decommissioned. It should be replaced with https://github.com/wikimedia/restbase/tree/master/doc instead.
This is the repository: https://phabricator.wikimedia.org/diffusion/CIDR/
This is the file: https://phabricator.wikimedia.org/diffusion/CIDR/browse/master/org/wikimedia/doc/default.html