Updated doc [ci skip]
Updated docblock
Normalized case of PHPDoc's tag [ci skip]
Added AttributeFilters\Regexp::getRegexp()
Configurator: implemented __isset() to check whether a plugin has been loaded
TagProcessing: added a couple more tests for out-of-bounds tags
Renamed the needs-nodejs test group to needs-js as it works with either nodejs or d8
Added Configurator::__isset() tests
Added MediaEmbed plugin