What formats are supported in OpenApi v2 for relative URLs?

I'm working on Swagger docs currently on V2, and using the 'externalDocs' object to link to supplemental API documentation that I'm developing.  Using relative URLs in the externalDocs is highly advantageous, as I can link to additional Markdown files in my Swagger directory.  However, the code running at https://editor.swagger.io/ doesn't seem to like relative URLs, and just in the last week seems to have become more restrictive about the relative URLs it disallows - now I can't get any form of relative URL to pass validation.

Swagger v3 does support relative URLs as per https://datatracker.ietf.org/doc/html/rfc3986, but there's no mention of relative URLs in v2.  Can anyone speak to what is possible in v2 for relative URLs?