There are various web specs which use [SetValueInBuffer](https://webidl.spec.whatwg.org/#arraybuffer-write) directly (via WebIDL). These need to be updated and WPT tests written. Also, there are specs which do a [defensive copy of the bytes in a view](https://webidl.spec.whatwg.org/#dfn-get-buffer-source-copy) which can be avoided when the buffer is immutable. This technically is an as-if optimization, but it's probably worth updating the WebIDL and consuming specs to call this out anyway because otherwise people will not know to make this optimization. See [discussion in Matrix](https://matrixlogs.bakkot.com/TC39_Delegates/2025-02-19#L12-L29).