schema question

Hi,

This is a schema rather than an xslt question, but I hope you can help.

I'd like to define an element (complexType) that *must* contain certain
elements one or more times, but may additionally contain any other
elements.  Further, I need all elements to be albe to appear in any order.

I have a suspicion this can be done with some xs:group wizardry, but I
just can't seem to figure it out.  I'm hoping someone here can get me on
the right track.

Thanks,

pt.