I sometimes see people refer to file system paths (POSIX/Windows) as both URIs and URLs. I'm no file system buff, but I have yet to find a file system path that conflicts with my understanding of the URL format. That is, of course, given that it includes the scheme name (e.g. file://localhost/path/to/file.txt).
File system paths are most definitely URIs - I mean, what's not - so everyone referring to file system paths as URIs is inside the safe zone. But is it safe to call them URLs?
If the URL was defined by a single (non-obsolete) RFC, rather than being comprised of half a dozen specialized ones, I wouldn't have to ask this question.
C:\Windowsis an invalid URL and an invalid URI.file://support may be silently removed from Chromium and Chromium-based browsers soon. bugs.chromium.org/p/chromium/issues/detail?id=1299624