gistfile1.txt

    /** Set the port.

        The port of the URL is set to the specified
        which must have the <em>port</em> syntax:

        @li If the string is empty, the port is
        cleared including the leading colon (':'). If
        the port was the last remaining portion of
        the authority, then the entire authority is
        removed including the leading double slash ('//').
        Otherwise,

        @li If the string is not empty then the port
        is set to the given string, with a leading
        colon added.
        If the URL previously did not contain an
        authority (@ref has_authority returns `false`),
        then the authority is added including the
        leading double slash ('//').
        The string must meet the syntactic requirements
        of <em>port</em> otherwise an exception is
        thrown.

        @par ABNF
        @code
        port          = *DIGIT
        @endcode

        @par Exception Safety

        Strong guarantee.
        Calls to allocate may throw.

        @param s The string to set.
    */
    BOOST_URL_DECL
    basic_value&
    set_port(string_view s);