code: def get_html_keywords(index_page):
      
      keyword_lists = (
          keyword_list.split(",")
          for keyword_list in parse_meta(index_page, "keywords", "HTML")
      )
  
      # create SourceStrings from the list of keywords
      return [
          SourceString(keyword.strip(), source="HTML")
          for keyword in sum(keyword_lists, [])  # flattern the list
      ]
docs: Return list of `keywords` parsed from HTML ``<meta>`` tags.
  
      Args:
          index_page (str): Content of the page as UTF-8 string
  
      Returns:
          list: List of :class:`.SourceString` objects.