This is for the next generation of MCS/PCS (Page Content Service) page content.
The goal of this is to reduce the payload for references by replacing the <ol> tags that wrap references with a placeholder element (`<div>`?). To look for the reference <ol> tags we can use ol[typeof=’mw:Extension/References’].
Clients then can later request the reference list information of the same revision through another endpoint (e.g. `/page/references/:title/:rev`) and merge the content into each placeholder.
The placeholder element needs:
# a type to signify that it is a placeholder for references, so that clients could add onclick handlers if desired (`typeof`) and
# an identifier of the references list so that clients can find the right place in the DOM to replace the placeholder with the original `<ol>` tag (to get it in the original state). A client may also chose to add a new onclick handler on the `<ol>` tag for collapsing/opening the references list if desired.
* Web did experiments in this area - https://www.mediawiki.org/wiki/Reading/Web/Projects/Performance/Lazy_loading_references