In the mobile site, the references widget parses the HTML of the page to generate a structured data object representing all references in the page.
When a reference is clicked it shows a "ReferencesDrawer" widget showing the user the reference in place.
Given the references HTML accounts for 50% of the total page HTML and very few people [[ https://www.mediawiki.org/wiki/Lazy_loading_of_references_on_Russian_Wikipedia | view references on mobile and the fact that this would save our users many terabytes of data in a year]], we should not serve this by default and instead route requests for references to a special page and use the API when JavaScript is enabled to retrieve references when needed.
Further reading:
* https://www.mediawiki.org/wiki/Reading/Web/Projects/Performance/Lazy_loading_references