 class="argument">ATTRIBUTE</li>    <li class="argument lambda-list-keyword">&amp;REST</li>  </ul>  <a class="source-link" href="https://github.com/Shinmera/clip/blob/64eedbbf637a874080bfcd351b69ee6d58588d7f/conditions.lisp#L56">Source</a>  </header> <div class="docstring"><pre>Checks whether the given attribute is the only attribute on the node.

If it is not present, or not the only one, an error is signalled.
Otherwise, the attribute's value is returned.

See <a href="#FUNCTION%20CLIP%3ACHECK-NO-UNKNOWN-