Due to the evidence from CoffeeScript, I thought we agreed to remove all constructs from optional chaining except for x.?y, x?.[y] and x?.(y). However, in this thread, @claudepache mentioned that optional chaining deletion is not yet banned. We should make it an early error in the draft spec, shouldn't we? Are there any other constructs that are currently allowed besides those three? The ambiguity here is delaying proper implementation in Babel.