Crosscut

When formatting a syntax tree using postfix syntax, my first instinct was to start with the children in the upper-left, then indent their parent. So a function call looked like this:

argument
    function

I was going to expand that into a more complicated (and realistic) example and demonstrate how confusing this could get, but then realized that I could only reproduce the worst problems I encountered by using free-form structural editing. So the switch to restricted structural editing by itself solves a lot of issues.

So that's one less reason to switch away from postfix syntax, I guess. But I don't think this significantly weakens the overall argument, as postfix syntax generally doesn't interact well with restricted structural editing. And even if the worst problems are fixed, that still leaves us with the general weirdness of this unfamiliar representation.