[lacey]

Usually operators are defined as being left-associative, right-associative, or non-associative.

So e.g.,

a + b + c is interpreted as (a + b) + c because + is commonly left-associative

whereas

a ^ b ^ c is a ^ (b ^ c)

because languages that support ^ for exponentiation treat it as right associative.

For non-associative operators, parentheses are required if you have two operators at the same precedence, so I believe the grandparent is arguing that e.g. a + b - c should require parens to disbiguate in a language where + and - have the same precedence.