code: protected void fill(GroupContainerPopulator containerPopulator,
                          Object controlFactory,
                          CommandButtonConfigurer configurer,
                          List previousButtons) {
  
          Assert.notNull(containerPopulator, "containerPopulator");
          Assert.notNull(controlFactory, "controlFactory");
          Assert.notNull(configurer, "configurer");
  
          if (members.size() > 0 && isLeadingSeparator()) {
              containerPopulator.addSeparator();
          }
  
          for (Iterator iterator = members.iterator(); iterator.hasNext();) {
              GroupMember member = (GroupMember)iterator.next();
              member.fill(containerPopulator, controlFactory, configurer, previousButtons);
          }
  
          if (members.size() > 0 && isEndingSeparator()) {
              containerPopulator.addSeparator();
          }
  
      }
docs: Adds each member of this expansion point to a GUI container using the given container
  populator. Leading and trailing separators will also be added as determined by the
  appropriate flags set on this instance.
  
  {@inheritDoc}