This disallows putting URLs in topic titles for TL0 users, which means that:
If a TL-0 user puts a link into the title, a topic featured link won't be generated (as if it was disabled in the site settings)
Server methods for creating and updating topics will be refusing featured links when they are called by TL-0 users
TL-0 users won't be able to put any link into the topic title. For example, the title "Hey, take a look at https://my-site.com" will be rejected.
Also, it improves a bit server behavior when creating or updating feature links on topics in the categories with disabled featured links. Before the server just silently ignored a featured link field that was passed to him, now it will be returning 422 response.
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