A problem with semantic markup is when it doesn't do what you want, and you need to wig-wam it. Does this mean you actually wanted presentation markup? Or, since you are trying to convey meaning, does it mean that the semantics aren't rich enough to describe what you mean?
In this D2 example (https://d2-lang.com/assets/images/intro-example-a917149ff3b7...), the diagram is nicely designed to be centered on the nexus node crawler. But the choices of which side the tributary nodes are on is not. You might want cron below and ps->express below - or to the sides.
The grammar can be extended to accommodate this (maybe already has been), but what is the semantic meaning of above, below, left or right?
One semantic choice is made: the "persists" arc is unidirectional, and is presented left-to-right - a natural order for many languages.
(Technically, "declarative" needn't be "semantic", but arguably is the most useful one)