hallow swap that does not do reference tracking. If you embed a <code class="computeroutput"><a class="link" href="basic_regex.html" title="Struct template basic_regex">basic_regex</a></code> object by reference in another regular expression and then swap its contents with another <code class="computeroutput"><a class="link" href="basic_regex.html" title="Struct template basic_regex">basic_regex</a></code> object, the change will not be visible to the enclosing regular expression. It is done this way to ens