Panel not working

hi Guys,

     I am using the following code in XML view for Panel, but the> doesn't show up to expand or collapse. I have tried the code from the SAPUI5 Explored.

<Panel expandable="true" expanded="false" headerText="Panel with a header text">   

    <content>    

      <Text text="Lorem ipsum dolor st amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat" />

    </content>

  </Panel>

Thanks,