code: def convert_to_ssml(text, text_format):
      
      if text_format is None:
          return text
      elif text_format == 'plain':
          return plain_to_ssml(text)
      elif text_format == 'html':
          return html_to_ssml(text)
      else:
          raise ValueError(text_format + ': text format not found.')
docs: Convert text to SSML based on the text's current format. NOTE: This module
      is extremely limited at the moment and will be expanded.
  
      :param text:
          The text to convert.
      :param text_format:
          The text format of the text. Currently supports 'plain', 'html' or None
          for skipping SSML conversion.