differential equations – Asymptotic Output Tracking: Compensator properties

Asymptotic Output Tracking: Code Issues

The question is, rather, of a theoretical nature (practical applications can be viewed in the topic at the link).

Asymptotic Output Tracking is said to be based on the FeedbackLinearize command which has different Compensator properties.

Question:
What is “DecouplingMatrix”, what is its meaning and how can it be “pulled out” after synthesizing a linearizing feedback signal?