For (far too) many years, there has been no definitive abc standard. (Apologies!)
Software developers are unsure which features to implement and users are unsure which are supported by a given package.
Accordingly, I would like the abc user community as a whole to vote on which standard they would like adopted so that we can resolve the situation once and for all. When enough votes have been cast, I will publish the selected version as the definitive standard and update the website to reflect the popular choice.
Of course, (as now) there will be no absolute requirement for software developers to stick to the standard. However, with a definitive published standard, developers can state which features they support and if they provide any extensions. Meanwhile, users should find it easier to create and modify abc files that can be used portably by a range of software packages.
Please take a moment to vote on your choice. You can vote here or on the "learn abc" page or both (in the event of a split decision, votes in the forums, coming from registered users, may carry slightly more weight).
Thank you.
Chris