code: Set<CmsUUID> getOpenElementIds() {
  
          Set<CmsUUID> ids = new HashSet<CmsUUID>();
          for (CmsLazyTreeItem item : m_treeItems) {
              CmsVfsEntryBean entry = item.getData();
              if (item.isOpen()) {
                  ids.add(entry.getStructureId());
              }
          }
          return ids;
      }
docs: Collects the structure ids belonging to open tree entries.<p>
  
  @return the structure ids for  the open tree entries