This article is a follow up to PHP AND EXPONENT IN 2016. Roughly one year after that previous article, PHP development is proceeding at breakneck speeds and we have seen two minor versions pass (though v7.2 is in release candidate status). Here's how it affects Exponent CMS.
The current release of Exponent (v2.4.1) is compatible with PHP v5.3 through v7.1. However, it is not compatible with PHP v7.2 (this will be corrected in the v2.4.2 release). The next release of Exponent (v2.4.2) will be compatible with PHP v5.5 through v7.2. We'll drop support for PHP v5.3 and v5.4 in that release because they are simply too insecure and should not be used in a production environment. And even though we will support PHP v5.5 in the next release, it is no longer recommended for production use since it was marked 'end of life' over one year ago. PHP v5.6 and v7.0 will be supported by their organization through the end of 2018, at which point only PHP v7.1 or later would be recommended. Another reason to remove old PHP version support in Exponent is that many of our 3rd party libraries simply no longer support ancient versions of PHP.
While we're on the subject of obsolete software, many browser software versions have also been termed 'end of life' and it is strongly encouraged they NOT be used! This would include Internet Explorer versions less than v11 (Edge in Windows 10 is considered Internet Explorer v12/v13). A beneficial side effect to this is that recommended browser versions are all now HTML5 compliant...which means that Exponent shouldn't need to use patches/tweaks to support HTML5 non-compliant browsers.Therefore, in the near future (though not in v2.4.2), we will drop support for obsolete/ancient browsers, which in turn should speed up page loading a bit.
Exponent CMS Developer