/usr/share/php/Horde/Text/Filter/ is in php-horde-text-filter 2.3.3-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Horde/Text/Filter/Base.php
/usr/share/php/Horde/Text/Filter/Bbcode.php
/usr/share/php/Horde/Text/Filter/Cleanascii.php
/usr/share/php/Horde/Text/Filter/Cleanhtml.php
/usr/share/php/Horde/Text/Filter/Dimsignature.php
/usr/share/php/Horde/Text/Filter/Emails.php
/usr/share/php/Horde/Text/Filter/Emoticons.php
/usr/share/php/Horde/Text/Filter/Environment.php
/usr/share/php/Horde/Text/Filter/Exception.php
/usr/share/php/Horde/Text/Filter/Highlightquotes.php
/usr/share/php/Horde/Text/Filter/Html2text.php
/usr/share/php/Horde/Text/Filter/JavascriptMinify.php
/usr/share/php/Horde/Text/Filter/Linkurls.php
/usr/share/php/Horde/Text/Filter/Simplemarkup.php
/usr/share/php/Horde/Text/Filter/Space2html.php
/usr/share/php/Horde/Text/Filter/Tabs2spaces.php
/usr/share/php/Horde/Text/Filter/Text2html.php
/usr/share/php/Horde/Text/Filter/Translation.php
/usr/share/php/Horde/Text/Filter/Words.php
/usr/share/php/Horde/Text/Filter/Xss.php