tle="Options for POSIX Extended Regular Expressions">Options
        for POSIX Extended Regular Expressions</a>
</h4></div></div></div>
<p>
          Exactly one of the following must always be set for <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
          extended regular expressions</a>:
        </p>
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