Error format documentation for UIs / more consistent error format

Hi there,

I co-maintain Flycheck, an Emacs UI for linters and compilers (Flycheck runs compilers in the background and displays errors as squiggly underlines).

I'm in the process of updating the checker definition for jsonnet and I'm having trouble figuring out a regular expression that covers all error messages returned by jsonnet (in general we prefer when tools can report their errors in a machine-friendly format, such as JSON or XML, but IIUC jsonnet only supports human-readable output; correct?)

Is there documentation somewhere (sorry if I missed it!) about the format that error messages are expected to conform to? I went through the `.golden` outputs in the `test` directory, but it seems that some errors do not include line or column numbers at all (e.g. https://github.com/google/jsonnet/blob/master/test_suite/error.function_no_default_arg.jsonnet.golden). I understand that static errors have a single location and that runtime errors have a stack trace; correct?

It would be great if jsonnet could consistently print at least one location for each error, but we'll adjust even if it can't :)

Thanks!