Composite as dataselect source?

Hi!

I'm trying to use composite input type as a source for dataselect. And it doesn't work. Am I doing something wrong?

This is how composite input field looks:

<perch:content id="date_course" type="composite" for="date course"  join=", " />

And dataselect in another template:

<perch:content id="course" label="Kurz" type="dataselect"
  page="/2013/pages/kurzy.php"
  region="Termíny kurzů" options="date_course"
  title="true" />