 or
                <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code>
                and <span class="emphasis"><em>U</em></span> contains an element that is <span class="emphasis"><em>not </em></span><code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> or
                <code class="computeroutput"><a class="link" href="ba