Non-pure
This extension depends on Lua modules (that is Lua code) that are non-pure. Code that is said to be non-pure is integrated with the server or other parts of the run-time. That means the Lua code can't be ripped out of the environment and uploaded as a module page at some wiki, even if they happen to run Mediawiki and has the Scribunto extension. The code must be integrated into the environment as an extension.
This is contrary to Lua modules that are pure. Such Lua modules can be uploaded to wikis that run Mediawiki and has the Scribunto extension, and with small changes they will work.