de>)
        requires that the following parser (<code class="computeroutput"><span class="identifier">b</span></code>)
        match the input or an <code class="computeroutput"><span class="identifier">expectation_failure</span></code>
        is emitted. Using a client supplied <code class="computeroutput"><span class="identifier">on_error</span></code>
        handler, the exception can be serviced by calling the handler with the source
        iterators and context at which the parsing failed can be re