    If at any stage the call-back function returns <span class="emphasis"><em>false</em></span>
                    then the grep operation terminates, otherwise continues until
                    no further matches are found. Returns the number of matches found.
                  </p>
                </td>
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                  <p>
                    <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">int</span>
                    <span class="identifier"