https://www.w3schools.com/tags/tag_article.asp says that the <article> tag is for forum posts, blog posts, news stories and comments.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/article says they are for forum posts, magazine or newspaper articles and blog entries.
Presumably, the div that currently has the classes "flow-post-content" and "mw-parser-output" would become an article.