@Override
  @NotNull
  public Collection<StructureViewTreeElement> getChildrenBase() {
    final XmlDocument document = getElement().getDocument();
    List<XmlTag> rootTags = new ArrayList<>();
    if (document != null) {
      for (PsiElement element : document.getChildren())
        if (element instanceof XmlTag) rootTags.add((XmlTag)element);
    }

    Collection<StructureViewTreeElement> structureViewTreeElements =
      getStructureViewTreeElements(rootTags.toArray(XmlTag.EMPTY));

    Collection<StructureViewTreeElement> dtdStructureViewTreeElements = null;
    final XmlProlog prolog = document != null ? document.getProlog():null;
    if (prolog != null) {
      final XmlDoctype doctype = prolog.getDoctype();

      if (doctype != null) {
        final XmlMarkupDecl xmlMarkupDecl = doctype.getMarkupDecl();
        if (xmlMarkupDecl != null) {
          dtdStructureViewTreeElements = DtdFileTreeElement.collectElements(xmlMarkupDecl);
        }
      }
    }

    if (dtdStructureViewTreeElements != null) {
      final ArrayList<StructureViewTreeElement> result = new ArrayList<>(
        dtdStructureViewTreeElements.size() + structureViewTreeElements.size()
      );

      result.addAll(dtdStructureViewTreeElements);
      result.addAll(structureViewTreeElements);
      structureViewTreeElements = result;
    }
    return structureViewTreeElements;
  }
@Override
  @NotNull
  public Collection<StructureViewTreeElement> getChildrenBase()