Roots designate the components to choose as "garbage collection roots" for the object graph.

The purpose of the Roots/garbage collection mechanism is to allow you to pass to the injector more bindings than strictly necessary and defer the choice of what specific components to construct from those bindings. Effectively, this selects a *sub-graph* of the largest possible object graph that can be described by bindings.

Tests in distage-testkit and roles in distage-framework are built on this mechanism. distage-testkit's test cases designate their parameters as roots and instantiate only the sub-graph required for a given test case. distage-framework's roles are effectively just allow you to choose root components and pass them command-line parameters.