/usr/share/php/HTMLPurifier.kses.php is in php-htmlpurifier 4.3.0+dfsg1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/php/../php-htmlpurifier/library/HTMLPurifier.kses.php
/usr/share/php/../php-htmlpurifier/library/HTMLPurifier.kses.php