+ or [.foo=a, .bar=b] or [ [1]=a, [2]=b]
+ That last doesn't parse easily, unless we require tags... not a good idea.
+ [ .[1] = a, .[2] = b ] ?? Maybe.
+ or () to group, [] for index. To (.foo=a) ( [1] = b )
+
+ I think that last works. () might almost be optional
+ .foo=a
+ is an expression means a structure with a .foo field assined to 'a'
+ [3] = 2
+ is an array for at least 4 elements with 4th set to 2.
+