'This method is called with the source of each downloaded :term:`HTML` file, before
it is parsed for links and images. It is called after the cleanup as
specified by remove_tags etc.
It can be used to do arbitrarily powerful pre-processing on the :term:`HTML`.
It should return `soup` after processing it.
`soup`: A `BeautifulSoup <https://www.crummy.com/software/BeautifulSoup/bs3/documentation.html>`_
instance containing the downloaded :term:`HTML`.'

def preprocess_html(self, soup):

    return soup
