https://www.11ty.dev/docs/config/#linters are super cool, but I was hoping to have a linter for the raw input files so I could do a front-matter linter which would throw errors or otherwise report if a file was missing a "required" field in a file's front-matter.

Is something like that possible, or should I try and do that while defining a custom collection?
Or should it be something that I write separately using glob and grey-matter as a separate script?