//var %foo = bar | echo -a $+(test,123,(,%foo,),xyzzy,(,plugh,))
> test123(,%foo,)xyzzy(,plugh,)
Same deal with $eval() aka $().
Seems that parenthesis within these identifiers (and possibly others) creates a nesting protection between parameters.
Kind of like the nesting peren protection we enjoy when using commas and curly brackets {} within a regular expression pattern.
Just wasn't expecting this. Maybe it's useful? Has it been like this a very long time?