 and <code class="code">b</code>. To help efficiency, it uses a cutoff: if the
    distance <code class="code">d</code> is smaller than <code class="code">cutoff</code>, it returns <code class="code"><span class="constructor">Some</span>&nbsp;d</code>, else
    <code class="code"><span class="constructor">None</span></code>.</p>

<p>The distance algorithm currently used is Damerau-Levenshtein: it
    computes the number of insertion, deletion, substitution of
    letters, or swapping of adjacent letters to 