code: public void buildNestedClassesSummary(XMLNode node, Content memberSummaryTree) {
          MemberSummaryWriter writer =
                  memberSummaryWriters.get(VisibleMemberMap.Kind.INNER_CLASSES);
          VisibleMemberMap visibleMemberMap =
                  getVisibleMemberMap(VisibleMemberMap.Kind.INNER_CLASSES);
          addSummary(writer, visibleMemberMap, true, memberSummaryTree);
      }
docs: Build the summary for the nested classes.
  
  @param node the XML element that specifies which components to document
  @param memberSummaryTree the content tree to which the documentation will be added