Preface:Not sure if this is the right forum section.
I was rather dissatisfied with the available Assembly (x86-64) Syntax Definitions in the community at the moment,
in particular lack of new registers and new instruction sets was the catalyst.
So here is present you the brand new, updated Assembly Syntax Definition published under BSD License.
All instructions and register published and present in the Intel documentation as of 2/26/2013.
Also includes all NASM directives.
Constructive criticism is VERY welcome and in fact encouraged as it is no easy task to cover over 700 pages of documents without making a single mistake.