Should OpenAPI highlight the possibility of using the data URL scheme for external examples?

[hudlow]

Originally raised here: https://github.com/OAI/OpenAPI-Specification/pull/4647/files#r2135992019

My baseline assumption is that the data-URL-scheme is already perfectly valid as a URI for externalValue in an Example Object. As far as I know we don't enumerate valid URL schemes that could be used in a URI, so there are plenty of schemes that are valid as far as OpenAPI is concerned but probably not resolvable by most tooling. (Without getting into the broader question of when you can treat a URI as a URL...)

For example, I assume ftp://example.com/foo.png is a perfectly valid URI for an externalValue but not something most tools would attempt to resolve.

What I'd like to resolve here is:

1. Am I right that this is already valid?
2. If we think this is useful and not an anti-pattern should we add examples showing its usage and its utility?
3. Should we go out of our way to suggest that tooling (in... 3.??) ought to be able to resolve data URLs in some way?

Something like:

externalValue: "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAIAAAD91JpzAAAABGdBTUEAALGPC_xhBQAAADhlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAAqACAAQAAAABAAAAAqADAAQAAAABAAAAAgAAAADO0J6QAAAAEElEQVQIHWP8zwACTGCSAQANHQEDqtPptQAAAABJRU5ErkJggg%3D%3D"`