* primary - The content on this page is a primary source
* secondary - The content on this page is high quality, but which is primarily research based and may thus be tainted by unknown sources
* bot - The content on this page is mostly automatically generated by one or more ML models with some human curated improvements
HTML elements can also have data-content-quality to override the page level metadata. So if you have a primarily sourced paragraph.
Search engines can index this signal. Sites that claim primary, but which frequently are provably wrong or bot generated can be penalized.
(edited for formatting)