These are the readme of the ParamProcessor extension.
Extension page on mediawiki.org: https://www.mediawiki.org/wiki/Extension:ParamProcessor
The ParamProcessor extension, formerly known as Validator, is a parameter processing framework that provides a way to declaratively define a set of parameters and how they should be processed. It can take such declarations together with a list of raw parameters and provide the processed values.
Notes on installing ParamProcessor are found in the file INSTALL.