is more data, and that the
            implementation will perform a subsequent call to `get`.
            A value of `false` means there is no more body data.

        @li If `ec` contains an error code, the return value is ignored.

        @param ec Set to the error, if any occurred.
    */</span>
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span