Popper is built using an extensible core, which provides the foundation used to deliver all the functionalities offered by the library.
All the useful functionalities provided by the library are implemented as Popper modifiers. They are plugins, or middlewares, that can hook into the lifecycle of Popper, and add additional logic to the positioning operations provided by default by Popper. They effectively "modify" the popper state in some fashion, adding functionality, hence the term "modifiers".
