There are three different common standards: HR Open Standards Candidate, schema.org and JSON Resume. HROS (which does XML and JSON) is used as a data exchange format between enterprise ATS and HRIS it's very comprehensive and is very detailed (perhaps too detailed). Schema.org seems mostly like Google and friends just making something up (without even trying to work with other existing standards) and trying to get everyone to use it. JSON resume is about what it sounds like it is. Oh, and then there are various de facto standards where ATSes that work with job boards like Indeed or data vendors like People Data Labs... So there's a lot of standards. The problem is:

a good standard is one everyone uses.

Personal opinion: resumes are actually kind of hard. I've personally been involved in HR Open Standards and even though it is a very complete standard, it's still hard to map real world resumes into the format sometimes. There is a shocking amount of ambiguity, and a shocking amount of adjacent standards (some of those have been adopted) for describing work history, education, certifications, people and workplaces.

So... most of the industry just parses resumes into some internal schema, and a lot of employers make job seekers enter their education and history on a job application form so they get it their way. It's really messy. Hope that helps.