qr{(\A (?: .* / (?: \.\.?\z )? )? [^/]* )}msx;

##</code><code>##

qr{(\A
    (?:
        [a-zA-Z]:
        |
        (?:\\\\\\\\|//)[^\\\\/]+[\\\\/][^\\\\/]+
    )?
    (?:.*[\\/](?:\.\.?\Z(?!\n))?)?
    .*
)}msx;