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 _write_header(self, indent: int) -> None:
      self.write("<thead>", indent)
  
      if self.fmt.header:
          self._write_col_header(indent + self.indent_delta)
  
      if self.show_row_idx_names:
          self._write_row_header(indent + self.indent_delta)
  
      self.write("</thead>", indent)
  
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 19 for calling the HTMLFormatter obj's underlying member method code with example usage: obj._write_header(indent) without return types