class_docstr: Internal class for formatting output data in html.
  This class is intended for shared functionality between
  DataFrame.to_html() and DataFrame._repr_html_().
  Any logic in common with other output formatting methods
  should ideally be inherited from classes in format.py
  and this class responsible for only producing html markup.
code: def _get_columns_formatted_values(self) -> Iterable:
      return self.columns
  
imports: from __future__ import annotations
  from textwrap import dedent
  from typing import TYPE_CHECKING, Any, Final, cast
  from pandas._config import get_option
  from pandas._libs import lib
  from pandas import MultiIndex, option_context
  from pandas.io.common import is_url
  from pandas.io.formats.format import DataFrameFormatter, get_level_lengths
  from pandas.io.formats.printing import pprint_thing
label_desc: Use image node_id 8 for calling the HTMLFormatter obj's underlying member method code with example usage: obj._get_columns_formatted_values() and returns: self