code: public Set<TreeNode> query(Query query) {
      return query.execute(Collections.singleton(root));
    }
docs: Run the supplied {@code Query} against this {@code ContextManager}'s
  root context.
  <p>
  The initial node in the queries traversal will be the node whose children
  form the root set of this {@code ContextManager}.  That is, the following
  code will select the root set of this instance.<br>
  <pre>
  public static Set&lt;TreeNode&gt; roots(ContextManager manager) {
  return manager.query(QueryBuilder.queryBuilder().children().build());
  }
  </pre>
  
  @param query the query to execute
  @return the set of nodes selected by the query