code: @SuppressWarnings("unchecked")
      public org.w3c.dom.Node ensureExistence(final org.w3c.dom.Node contextNode) {
          final Document document = DOMHelper.getOwnerDocumentFor(contextNode);
          final Map<String, String> namespaceMapping = new HashMap<String, String>(userDefinedMapping);
          namespaceMapping.putAll(DOMHelper.getNamespaceMapping(document));
          //node.dump("");
          return ((List<org.w3c.dom.Node>) node.firstChildAccept(new BuildDocumentVisitor(variableResolver, namespaceMapping), contextNode)).get(0);
      }
docs: Creates nodes until selecting such a path would return something.
  
  @param contextNode
  @return the node that this expression would select.