On: Delimiter-first code

[layer8]

Whether the marker is leading or trailing is orthogonal to whether the first/last marker is optional. And usually you want to have it optional in either case so that e.g. you can write `f(arg)` and don’t have to write `f(,arg)` or `f(arg,)`.

Hence it would be:

  leading-marker-list = [ element, *("-", element) ]