static List<StructureViewTreeElement> collectElements(final XmlElement element) {
    final List<StructureViewTreeElement> elements = new ArrayList<>();

    XmlUtil.processXmlElements(element, new PsiElementProcessor() {
      @Override
      public boolean execute(final @NotNull PsiElement element) {
        if (element instanceof XmlElementDecl ||
            element instanceof XmlEntityDecl) {
          elements.add(new DtdTreeElement((PsiNamedElement)element));
        }
        return true;
      }
    }, false);
    return elements;
  }
static List<StructureViewTreeElement> collectElements(final XmlElement element)