I have a couple of very Engineering focused Specs from before HTML was a thing. Namely, the OVF XML format and OVA file format (tarball of an ovf)

https://www.dmtf.org/standards/ovf

There are schemas on there and PDF's describing the standard. I can't import the schema directly. And also not the Specification site.

Especially, such old specs have kinks that people cannot even find when they read it themselves, so having an assistance to parse those and check results is an absolute game changer.