The current implementation enables/disables the extensions that we bundle in the Enhance PHP packages but don't enable by default.
An update is coming to this feature which will let you provide arbitrary extensions for your customers to enable - the system will scan the extension dir (for whichever PHP version the website is using) for .so files and will allow any of those extensions to selected by the customer.
You can do this already by adding the "extension" directive to the php.ini but it's only possible to load one custom extension per website using this method.
We also automatically load the monarx.so file if Monarx is installed on your system.
