 <a href="dart-core/String-class.html">String</a> or a <a href="dart-async/Future-class.html">Future</a>
completing with a <a href="dart-core/String-class.html">String</a>. The <a href="dart-core/String-class.html">String</a> must exist in the list of
protocols.</p>
<p>If <code>compression</code> is provided, the <a href="dart-io/WebSocket-class.html">WebSocket</a> created will be configured
to negotiate with the specified <a href="dart-io/CompressionOptions-class.html">CompressionOptions</a>. If none is sp