This is the main aggregator for all implementation code shared between modules. Each module contains one or more service interfaces, exposed statically using "X_" prefixed classes. Core modules will define their API interfaces, their static accessor, and often a "plain-jre" default implementation which can be replaced by injection override. There must be zero external dependencies in any core modules. A low-performance, low-feature default is preferred over thick, dependency-ridden shared inherits.