class="keyword">let</span> attachment_metadata: <a href="index.html#type-t">t</a> <span>=&gt;</span> option(<a href="../../../../../../Object/Of_strings/index.html#type-t">Object.Of_strings.t</a>);</code></dt><dd><p>Upon successful attach, this field is populated with any information returned by the attach operation that must be passed into subsequent Wait_for_attach or Mount calls. This field must only be set by the entity completing the attach operation, i.e. the external_attacher.</p></dd></dl><dl><dt cl