tax_option_type.html" title="syntax_option_type">flag
        <code class="computeroutput"><span class="identifier">egrep</span></code></a> set, then the
        expression is treated as a newline separated list of <a class="link" href="basic_extended.html#boost_regex.posix_extended_syntax">POSIX-Extended
        expressions</a>, a match is found if any of the expressions in the list
        match, for example:
      </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special"