class_docstr: Given a block of HTML, group the content under the preceding
  heading tags which can then be used for creating an index
  for that section.
code: def __init__(self, *args, **kwargs) -> None:
      super().__init__(*args, **kwargs)
  
      self.data: list[ContentSection] = []
      self.section: ContentSection | None = None
      self.is_header_tag = False
      self._stripped_html: list[str] = []
  
imports: from __future__ import annotations
  import json
  import logging
  import os
  import re
  import subprocess
  from html.parser import HTMLParser
  from typing import TYPE_CHECKING
label_desc: Use image node_id 1 to create a new ContentParser object from inherited base classes: HTMLParser with example: obj = ContentParser()