Feature summary:
Have an option (checkbox) in Special:BlockedExternalDomains to specify for each domain if the block is enabled in all namespaces (box not checked) or only in mainspace (box checked).

Use case(s):
On fr-wp, we often want to forbid the use of some sources in the articles, because they lack reliability or are used for spam. But we still need to use them in talkpages; we can't anymore. In fact, in most cases, we only want to forbid a domain to be added in the mainspace; only in some specific cases of spam we want a domain not to be added anywhere.

Benefits:
Removing an irritating downside of adding a website to MediaWiki:BlockedExternalDomains.

Note:
Limiting filtering to mainspace is not currently possible with Special:BlockedExternalDomains, but we can use directly AbuseFilter for that. However, this is not a good practice for the following reasons:

• it's less practical that MediaWiki:BlockedExternalDomains
• AF can be edited by less people than MediaWiki:BlockedExternalDomains
• Using AF for blacklisting would mean split again where the blacklisted websites are stored (some are already on MediaWiki:Spam-blacklist and some on Special:BlockedExternalDomains)