Requested feature overview description.

Unlike with posts, e621 wiki pages currently don't allow any users to provide an edit summary/reason. Edit summaries have been a standard for wikis on the Internet for a long time, being used on Wikipedia, all Wikia/Fandom wikis, and TV Tropes, among many others.

Adding an edit summary/reason text field underneath the main text box and either above or next to the "Save" and "Preview" buttons in edit mode would give users the ability to explain their edits. Examples of these summaries/reason would include stuff like "Spelling corrections." or "Added a thumbnail to show an example of the tag." The edit summaries/reasons would be displayed in a wiki page's history under a column next to the "Last edited" column. Edit summaries/reasons would also have limited DText support, primarily links that would be clickable on the history pages. (e.g. "Removed thumbnail; post #6268 is not an example of cute.")

Why would it be useful?

To allow users to explain what they edited and why they did so, reducing the need to compare each and every version of a page.

This would also be especially useful for admins editing the DNP list and the Conditional DNP list, allowing them to explain who has been added and/or removed from them, or what conditions have changed. This would eliminate the need for users to make version comparisons to see the changes to those lists in particular. (e.g. "Added FurryArtist1234 / FurMeister / Fluffy McFlufftail, e621isnotforme, and DontRepostMePlz to the list; removed ItsOKToPostMeNow from the list; changed LiterallyExceptionalArtist's DNP conditions.")

What part(s) of the site page(s) are affected?

The wiki's edit mode (https://e621.net/wiki/edit/insert_tag_here) and history pages (https://e621.net/wiki/history?title=insert_tag_here).

+1. As an avid wiki editor in a lot of other fandom sites, as well as here of course, this would be incredibly useful to not only the editors but also outside parties, like mods or other users.