Framework Utilities Layer
Principle:
In order to properly drive and manipulate all dependencies of the SUT, often controlling the GUI of the SUT alone isn't enough.
The Utilities layer's responsibilities lie with exposing an interface to control all SUT's dependencies from within the different horizontal layers of the test framework.
Aside from the SUT's dependencies, this layer can also contain modules like logging, taking screenshots, recording screen captures, ...
This vertical layer of the test framework is the prime candidate for developing more general utility libraries that could be used across different projects.
Since this layer's interface will also be exposed to the highest horizontal level of the framework, the test scripts,
it should integrate smoothly into the interface of the functional layer.
Keep in mind that the combination of the utility and the functional layer's interface become the DSL through which your test scripts will drive the entire SUT.
Readability is key.