I am not talking about operator precedence, that’s a separate thing. Consider the parsing of math expressions, where juxtaposition of terms denotes multiplication unless it can be interpreted as something else. So f(x+2) is function application, whereas 3(x+2) is multiplication. With a PEG, you just write a standard expression grammar with an additional choice at the end for the implicit multiplication. With a conventional parser, this is much more difficult – you have to explicitly list all the different ways that terms could be next to each other without meaning something else.

We absolutely order more likely / preferred options before other options. Codifying that as a short circuit optimization is a feature.

> But that’s not how humans writing code generally think about ambiguous expressions. You can see that by how few precedence rules programmers tend to internalize

I'd argue that it is how humans think about ambiguous syntax, except in the special case of operator precedence, which is the most complex example. A more salient example to me would be, say, the case of an ‘else’ block after a double-‘if’:

  if (c) if (d) X; else Y;

It's technically ambiguous, but you only need to run into it once, see how your IDE auto-formatter indents it, and then you've internalized the precedence rule immediately.