old_contents: from __future__ import absolute_import
  
  from .attribute import (html_attribute, boolean_html_attribute,
                          int_html_attribute, float_html_attribute,
                          list_html_attribute)
  from .block import Division, Paragraph, Preformatted
  from .document import (Document, HTMLRoot, Head, Body, Title, Meta, Script,
                         HeadLink, Main)
  from .element import Element, VoidElement, is_element
  from .form import (Form, Input, TextInput, PasswordInput, NumberInput,
                     DateInput, TimeInput, SearchInput, FileInput, HiddenInput,
                     SubmitButton, Button, TextArea, Select, OptionGroup, Option)
  from .generator import (Generator, NullGenerator, IteratorGenerator,
                          ChildGenerator, HTMLChildGenerator,
                          JoinGenerator, HTMLJoinGenerator)
  from .image import Image
  from .inline import (Span, Highlight, Strong, Alternate, Emphasis, Small,
                       LineBreak)
  from .link import Link
  from .list import (OrderedList, UnorderedList, ListItem, DescriptionList,
                     DescriptionDefinition, DescriptionTerm)
  from .structure import (Section, Article, Navigation, Aside, Header, Footer,
                          Heading)
  from .table import (Table, TableHead, TableBody, TableRow, TableHeaderCell,
                      TableCell,
                      ColumnGroup, Column)
  from .time import Time
  
new_contents: from __future__ import absolute_import
  
  from .attribute import (html_attribute, boolean_html_attribute,
                          int_html_attribute, float_html_attribute,
                          list_html_attribute, data_attribute)
  from .block import Division, Paragraph, Preformatted
  from .document import (Document, HTMLRoot, Head, Body, Title, Meta, Script,
                         HeadLink, Main)
  from .element import Element, VoidElement, is_element
  from .form import (Form, Input, TextInput, PasswordInput, NumberInput,
                     DateInput, TimeInput, SearchInput, FileInput, HiddenInput,
                     SubmitButton, Button, TextArea, Select, OptionGroup, Option)
  from .generator import (Generator, NullGenerator, IteratorGenerator,
                          ChildGenerator, HTMLChildGenerator,
                          JoinGenerator, HTMLJoinGenerator)
  from .image import Image
  from .inline import (Span, Highlight, Strong, Alternate, Emphasis, Small,
                       LineBreak)
  from .link import Link
  from .list import (OrderedList, UnorderedList, ListItem, DescriptionList,
                     DescriptionDefinition, DescriptionTerm)
  from .structure import (Section, Article, Navigation, Aside, Header, Footer,
                          Heading)
  from .table import (Table, TableHead, TableBody, TableRow, TableHeaderCell,
                      TableCell,
                      ColumnGroup, Column)
  from .time import Time
  
subject: add data_attribute to htmlgen root package