For those who may not be aware, the next version of PHP after 5.6 is designated 7.0.
Kiwitrees has been fully compatible with PHP 5.6 since version 3.1.1, but has NOT been thoroughly tested on PHP 7.0, So I cannot recommend or provide adequate support for its use yet.
PHP 7.0 has been available since 3rd December 2015, and the latest variant (7.0.2) since 7th January 2016. So in PHP terms it is still VERY new.
PHP 5.6 was released on 28th Aug 2014, and is currently up to variant 5.6.17, released: 7th January 2016. It will be fully supported by PHP until 31 Dec 2016, with security support until 31 Dec 2018, which is actually 28 days longer than ver. 7.0, so there is no compelling reason to rush into upgrading to 7.
However, full testing of kiwitrees on PHP 7 has now started, and I hope that the next release (3.2.1?) will be fully compatible with it. There is currently no planned release date for kiwitrees 3.2.1, but probably 3 4 months from now.