Hello igears,
Self-referencing tag
To add a self-referencing tag add the page URL (the one set in the URL to Connect field) in one of the 10 URL fields available per connection (and set the related language, script, or geo-target).
Setting en-eu and similar group anotations
Hreflang uses ISO 3166-1 alpha-2 and “eu” is not an officially assigned code element for the region.
See:
https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#Officially_assigned_code_elements
https://developers.google.com/search/docs/specialty/international/localized-versions?hl=en&visit_id=638118745900323738-3340489383&rd=2#language-codes
https://moz.com/community/q/topic/30932/which-hreflang-tag-to-use-for-eu-domain
