Safari (Mac and iOS) does not permit functions named "𝝙". Does this break the spec?

Question

Safari (Mac and iOS) does not permit functions named "𝝙" (U+1D6AB, Mathematical Bold Greek Capital Delta).

AFAIK, Valid identifiers must have the derived core property "ID_Start".

"𝝙" appears to meet this criteria.

Does this break the spec?

function 𝝙(a, b) {
  return a-b
}
console.log(𝝙(2, 1)) // 1 in Chrome and FF; "Script error" in Safari

Interestingly, Safari does accept "Δ" (U+0394, Greek Capital Letter Delta) as a valid identifier:

function Δ(a, b) {
  return a-b
}
console.log(Δ(2, 1)) // 1 in Chrome and FF and Safari

I think it might be something to do with the former character being in the Astral Plane.

Answer 1

I think this is the bug. It was fixed in March and (presumably) hasn't made it out into released versions of browsers.