Question regarding DSD

Folks, I have a quick question regarding DSD as well..

I looked carefully at http://www.brics.dk/DSD/dsddoc.pdf
I especially looked at page 21, 22 of the specification which seems to
describe the crux of the algorithm. I have the following question..

I do not find how the validation will work for a content expression such
as ((a, b)*, a?) which I believe can be written as:

<Sequence>
  <ZeroOrMore>
    <Sequence> <Element Name="a"/> <Element Name="b"/> </Sequence>
  </ZeroOrMore>
  <Optional> <Element Name="a"/> </Optional>
</Sequence>

My question is will this validate the list of elements, say <a/>

thanks and regards - murali.