. Throwing an exception could allow the operation to be
    cancelled gracefully. On the other hand, it would probably be
    inappropriate to throw and <i>handle</i> exceptions in the inner
    loop of this computation because that could have a significant
    performance impact.  The guideline mentioned above has a grain of
    truth in it: in time critical code, throwing an exception
    should <em>be</em> the exception, not the rule.</p>

    <h3>How should I design my exception classes?</h3>

    <ol>
