/usr/share/php/HTMLPurifier.func.php is in php-htmlpurifier 4.4.0+dfsg1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/php/../php-htmlpurifier/library/HTMLPurifier.func.php
/usr/share/php/../php-htmlpurifier/library/HTMLPurifier.func.php