We're always having to remind visual language designers that they need some secondary notation. (Otherwise known as "comments", for any non-CDs readers stumbling across this). You might say that, up until this point, almost everything has been secondary notation because the execution semantics of my representation has been vague-to-non-existent.
However, in a remarkable display of self-discipline, I have created a secondary notation mechanism before starting on the execution semantics. Here's what it looks like at this stage: