DB<103> '"a\\"b"' =~  / " (?: [^"] | \\" )* " /x ; print $&        # nonsense
"a\"

  DB<104> '"a\\"b"' =~  / " (?: \\" | [^"] )* " /x ; print $&        # better
"a\"b"

  DB<105> '"a\\"b"' =~  / " (?: \\\\ | \\" | [^"] )* " /x ; print $& # best
"a\"b"