I follow the development of music notation software. (I'm not a developer myself; I'm a user.) To answer questions like this, people in every development project I've come across recently cite one particular reference book that was recently published:
Behind Bars: The Definitive Guide to Music Notation, by Elaine Gould, Alfred Music, 2011.
Perhaps you should consult that source.
The description of the book says:
In the most thorough and painstakingly researched book to be published
since the 1980s, specialist music editor Elaine Gould provides a
comprehensive grounding in notational principles.
Behind Bars covers everything from basic rules, conventions and themes
to complex instrumental techniques, empowering the reader to prepare
music with total clarity and precision. With the advent of computer
technology, it has never been more important for musicians to have
ready access to principles of best practice in this dynamic field, and
this book will support the endeavors of software users and devotees of
This seminal and all-encompassing guide encourages new standards of
excellence and accuracy and, at a weighty 704 pages, it is supported
by 1,500 music examples of published scores from Bach to Xenakis.