<esi:vars>
  <img src="http://www.example.com/$(HTTP_COOKIE{type})/hello.gif" />
  <img src="http://www.example.com/$(HTTP_COOKIE{does_not_exist}|'default_value')/hello.gif" />
  <img src="http://www.example.com/$(HTTP_HOST)/hello.gif"/>
  <img src="http://www.example.com/$(HTTP_ACCEPT_LANGUAGE{en})/hello.gif"/ >
</esi:vars>