Check schemas embedded in files

There are multiple times when we (the JSON Schema team) would like to be able to validate JSON embedded in other files, such as markdown. (Specifically, JSON Schema examples in our docs and website.)

I imagine it would work by allowing the following:

• Specify what files should be inspected
• Identify which fragments of the files are JSON (This may need different approaches per format, potentially with a way to self declare the wish to be validated)
• Process such fragments which self-identify which Schema they should be validated with (such as a standard meta-schema)
• Optionally take an argument/s which specifies a default JSON Schema to be used for all fragments within a given file/glob of files

Please do reach out to me on Slack or @Julian. I likely won't see follow up comments here directly as I've declared GH notificaiton bankruptcy. Thanks.

The issue names no files, tests, or entry points. Begin by clarifying supported file formats, fragment identification, schema selection, and CLI configuration. Done means embedded JSON fragments can be discovered and validated against explicit or default schemas.