What is the formal specification for the output files generated by force:apex:test:run ?

[RupertBarrow]

Is your feature request related to a problem? Please describe.
sfdx force:apex:test:run -r junitgenerates output files described in here (https://developer.salesforce.com/blogs/2021/04/clearer-apex-commands) to describe test results and code coverage.
What is the formal specification for these files ?
Where are their schemas defined ?
Are these compatible with test summary tools and code coverage report solutions which expect JUnit input format files ?

What are you trying to do
I'm trying to consume the output of sfdx force:apex:test:run -r junit to display Github Checks displayed by solutions such as Code Coverage or JUnit Coverage Report (https://github.com/marketplace/actions/junit-coverage-report)

Describe the solution you'd like
I would like to be able to generate output files which adhere to a standard, in this case the JUnit XML schema, and a code coverage format such as Cobertura XML, Jacoco XML.

Describe alternatives you've considered
None.

Additional context
I'm looking to inject results into Github Actions CI, so :

• produce a summary compatible with Github Checks to display in a PR
• add Github Annotations to code to point out lines of code covered/uncovered by tests

[git2gus]

This issue has been linked to a new work item: W-12347811

[github-actions]

Thank you for filing this feature request. We appreciate your feedback and will review the feature at our next grooming or sprint planning session. We prioritize feature requests with more upvotes and comments.