code: function transformSpecialElement(tag, node) {
          if (node.children.length === 1 && t.isJSXExpressionContainer(node.children[0])) {
              if (tag === "ui5Control") {
                  renderer.renderControl(node.children[0].expression);
              } else {
                  error(node, "Unknown special element: '" + tag + "'.");
              }
          } else {
              error(node, "Only expressions supported in special elements.");
          }
      }
docs: Function for handlign special elements (tags).