input: def html_to_text(html_string: str) -> str:
      """ Convert an HTML string to plain text by removing all HTML tags.
      >>> html_to_text('<h1>Hello, World!</h1>')
      'Hello, World!'
      >>> html_to_text('This is <b>bold</b> text.')
      'This is bold text.'
      """
output:     import re
      return re.sub(r'<[^>]+>', '', html_string)