I did not see this anywhere else on the forums so I thought I would share. Many extras such as Quip that generate a list of items use templates for those items. The templates often are given an ID ("idx" is the common placeholder). Sometimes you need to apply an odd/even class to those items. If you want to do it within the template you can use modulus output filter:
<li class="[[+idx:mod:isequalto=`1`:then=`even`:else=`odd`]]">[[+body]]</li>
Hope that helps.