It seems the idea morphed over time as the ticket progressed. What started as a suggestion to check for a broken link in the editor, turned into only a well-formed URL check. So the feature is now misnamed, which is adding confusion to understanding what the feature does.

Also, while preventing "link rot" is a worthy goal, I don't see how this feature makes a contribution to that. A link must be good before "rotting", and this feature is merely checking a link in the editor.