<span class="char">'}'</span></code>. Otherwise,
        there is no point in proceeding and trying other branches, regardless where
        they are. The input is definitely erroneous. When this happens, an expectation_failure
        exception is thrown. Somewhere outward, the error handler will catch the
        exception. In our case, it is caught in our <code class="computeroutput"><span class="identifier">on_error</span></code>
        handler.
      </p>
<p>
        Notice too that we subclass the <c