CSD G4 requires that the new article be substantially similar to the old article. However patrollers that aren't admins cannot see deleted revisions.

PageTriage already detects if an article has been "previously deleted". This ticket is to explore the idea of expanding this detection to include...

• Detection of a previous AFD, by checking for the existence of an AFD page
• If previous AFD detected, and the page has been deleted before, there should be an API added to PageTriage to pull the top deleted revision, and then compare it to the current top revision, and provide a % wikicode match.
• This should either be run with a button, or run automatically.
• May or may not want to make this a pagetriage_page_tag (article metadata).

Todo

• add API - could add to pagetriagelist API (but then would calculate this all the time, and calculating it could be expensive), or could create a dedicated API (would only calculate this when needed)
• add to front end - could add a button to calculate this, or could auto calculate it when visiting the article, or could auto calculate it for everything and add it as a red article tag in Special:NewPagesFeed (pagetriage_page_tag / metadata are involved in the latter)
• decide if we also want to add similar support for "previous AFD". there is an afd_status page tag, but it only tracks current deletion tagging. There is a recreated tag, but it tracks all kinds of previous deletion, not just AFD.

Credit to @Samwalton9 for the idea