This 0.5.1 release of the primer is essentially a bug-fix for the example code in the 0.5 version. The code has been made more LRM compliant, however there are no semantic or methodological changes.
From the prior releases:
This release of the primer covers additional topics, such as "Making sequences phase aware" and "Simplifying the common reset case"
The UVM Library has introduced an important set of new features commonly referred to as “Run-Time Phasing.” This primer is an approach towards using these new features to meet the needs of a common verification use-case. As an additional reference, and for the reader’s convenience, a code example which fully implements the methods presented in the primer is included.