To compute diff-related credibility signals, we need the wikitext for the current rev id and its parent rev id. We need to be able to pass rvlimit=2 and rvprop=content to the revision API in order to get the contents of the last two revisions.

To understand this, pls try this API call (in postman)

https://en.wikipedia.org/w/api.php?action=query&prop=revisions&titles=Green_Island_(Rideau_River)&rvlimit=2&formatversion=2&format=json&rvprop=content|ids|timestamp

Here, rvlimit=2 gets the latest two contents.
ids and timestamp under rvprop is just for illustration. We will be fine with just content.

To get this API result via our utility, you will have to enhance the revision utility such that it can get content for rvlimit=2.