HTML Purifier 4.9.x is a maintenance release, collecting a yearof accumulated bug fixes plus a few new features. New featuresinclude support for min/max-width/height CSS, and rgba/hsl/hslain color specifications. Major bugfixes include improvementsin the Serializer cache to avoid chmod'ing directories, betterentity decoding (we won't accidentally encode entities that occurin URLs) and rel="noopener" on links with target attributes,to prevent them from overwriting the original frame.4.9.3 works around an infinite loop bug in PHP 7.1 with the opcodecache (and has one other, minor bugfix, avoiding using autoloadingwhen testing for DOMDocument presence). If these bugs do notaffect you, you do not need to upgrade.