In the action API, there are two ways to parse a page/revision: using action=parse, or using the rvparse parameter to action=query&prop=revisions. Similarly, there are two ways to get a diff: using action=compare, or using parameters such as rvdiffto to action=query&prop=revisions. And then there's action=expandtemplates versus the rvexpandtemplates parameter to prop=revisions. This is a somewhat annoying bit of code duplication.

Further, the prop=revisions versions of these features have somewhat strange behavior. rvparse forces rvlimit=1. rvdiffto and related parameters will sometimes output "notcached" with no way to directly handle the situation.

This, the 'rvdifftotext', 'rvdifftotextpst', 'rvdiffto', 'rvexpandtemplates', 'rvgeneratexml', 'rvparse', and 'rvprop=parsetree' parameters to prop=revisions are all deprecated, as are the similarly named parameters to prop=deletedrevisions, list=allrevisions, and list=alldeletedrevisions.