The primary goal of PHP6 was to implement full unicode support and drop mbstring. However, that took much longer than expected and multiple major features ended up getting backported to 5.3, 5.4 and 5.6; to the point that PHP 7 became the new feature version while PHP6 was worked on. They eventually gave up and PHP7 was released with unicode support built fairly deep, but basic string types and the like still being byte arrays.
PHP7 was PHP6, without the native and full unicode coverage requirement.
The primary goal of PHP6 was to implement full unicode support and drop mbstring. However, that took much longer than expected and multiple major features ended up getting backported to 5.3, 5.4 and 5.6; to the point that PHP 7 became the new feature version while PHP6 was worked on. They eventually gave up and PHP7 was released with unicode support built fairly deep, but basic string types and the like still being byte arrays.
PHP7 was PHP6, without the native and full unicode coverage requirement.