SIS">must match</i></span> our
      pattern is <span class="APPLICATION">adv</span>, together with the forward slashes. What comes after the
      <span class="QUOTE">"adv"</span> string is the interesting part.</p>
      <p>Remember the <span class="QUOTE">"?"</span> means the preceding expression (either a literal character or
      anything grouped with <span class="QUOTE">"(...)"</span> in this case) can exist or not, since this means either
      zero or one match. So <span class="QUOTE">"((er)?ts?|er