On initially cracking open the MDN guide¹, *so far* it kind of seems like it only means "It's structured as an S-expression". That's a bit disappointing. It's an understandable decision, as S-expressions make parsing easy— I've used this shortcut myself— but also, it seems this is preserving *only* the part of LISP people hate most. What do people complain about the most? What do LISP heads complain the most about other people complaining about? *It's the parentheses*.
¹ https://developer.mozilla.org/en-US/docs/WebAssembly/Guides/Understanding_the_text_format