Old versions settings for user custom extensions and disappeared related wiki pages

[Dboingue]

I have been looking for documentation about how to use and customize extensions, and I came across an older post on stackexchange, indicating this very site had a wiki at some point.

For example
https://webapps.stackexchange.com/questions/80239/how-to-change-the-edit-mode-in-stackedit-io-to-right-to-left-only-at-certain-row
And answer there with an intriguing more elaborate settings interface figure embedded is linking back to some wiki not to be found:
https://github.com/benweet/stackedit/wiki/UserCustom-extensions

I wonder why there is not such a wiki. And from the GUI of stackedit, perhaps could we share here the elements that existed both in the post visible settings shown, and or from the old wiki. About user custom-extension. syntax or how it works and what is still feasible.

I apologize if that has been asked before. I did make a first search in issues (open or closed). but there are a lot, and the first page did not seem to have something related.