[Zope] alternating colors based on sequence-index of outer loop

[John Hunter]

I have a folder called Sections that is filled with Section instances.
Each Section contains a variable number of students, and I want all
the students in a given section to have the same row color in my
table, with sections alternating colors.

I have nested dtml-in loops over the sections and students in each
section, and want the rows of my table to alternate in batches
depending on whether the outer loop is even or odd.  Basically, I need
to do a dtml-let in the outer loop that the inner loop will access,
but am having trouble with the syntax.

Here is some example dtml with pseudo code to set the default_color

      <dtml-in expr="Sections.objectValues('Section')" mapping>
          <dtml-if sequence-even>
             default_color="gray"
          <dtml-else>
             default_color="white"
          </dtml-if>  
         <dtml-in expr="_['sequence-item'].objectValues('Student')" mapping>
 	  <tr default_color>
		..Fill in the row..
	   </tr>
         </dtml-in>
      </dtml-in>


Thanks for any help,
John Hunter