This project was initially a part of lxml. Because HTML cleaner is designed as
blocklist-based, many reports about possible security vulnerabilities were
filed for lxml and that make the project problematic for security-sensitive
environments. Therefore we decided to extract the problematic part to a
separate project.

Important: the HTML Cleaner in lxml_html_clean is not considered appropriate
for security sensitive environments. See e.g. bleach for an alternative.