Hello,
Closes to documentation is this:
webcodingeasy.com/PHP-classes/Gener
...
unfortunately there is no configuration for disabled inputs and yes doing it on javascript only part is probably not a good idea in case javascript is disabled.
but honestly my current day job is not related to PHP anymore, for almost 2 years now, so I can't keep the class updated with new features, but if you are willing to pinch in, I can publish it on github and would gladly accept PRs and publish updated package here.
Adding such functionality should be straight forward, adding array containing disabled field, providing method to modify this array and then editing all *_type methods that generate input to check if this input should be disabled or not.