Input and relative paths

Quick question: is using relative paths with (back)slashes portable?

I see that both

    input a/b/c.mp
    input a\b\c.mp

work in macOS (so, I suppose, in *nix systems in general).
Can you please confirm that they both work in Windows, too?

Also, is it correct that the input command above searches only

(a) in the directory from which mpost is launched, but not in its
    subdirectories (so, it would find ./a/b/c.mp, but not ./x/y/a/b/c.mp);
(b) in a set of predefined directories, like /texlive/texmf/metapost,
    *and* in all of its subdirectories (so, it would find both
    /texlive/metapost/a/b/c.mp and /texlive/metapost/x/y/a/b/c.mp);

in that order? And this also in Windows?

Nicola


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http://tug.org/metapost/