They readme suggests that it supports PHP back to 5.3. PHP 7.2 and 8.0 were huge compatibility leaps for the language. None of my 5.3 codebases would run on 8.1, which the readme also suggests, and none of my PHP 8 codebases would run on 5.3. This must be using such a small subset of the language that it would be difficult for a human to maintain it. Especially considering that no third party library would ever be able to run on those two versions.