Requirements for SpeechSynthesisErrorEvent

[jugglinmike]

Chromium's implementation of SpeechSynthesisErrorEvent (at version 105) requires the utterance property in the SpeechSynthesisEventInit interface.

new SpeechSynthesisErrorEvent('d', {errror:'foo'})
VM456:1 Uncaught TypeError: Failed to construct 'SpeechSynthesisErrorEvent': Failed to read the 'utterance' property from 'SpeechSynthesisEventInit': Required member is undefined.
    at <anonymous>:1:1

Firefox's implementation (at version 105) behaves similarly:

new SpeechSynthesisErrorEvent('d', {errror:'foo'})
Uncaught TypeError: SpeechSynthesisErrorEvent constructor: Missing required 'utterance' member of SpeechSynthesisEventInit.
    <anonymous> debugger eval code:1

The only reference I can find to an initializer property with that name is 2018's gh-45, where it was added as a requirement for the SpeechSynthesisEvent. I can't tell if this was an omission at that time, a more recent (though undocumented) development in the design of this proposal, a bug in these implementations, or something else altogether. @foolip do you have any thoughts on this?

[foolip]

The utterance member is required because SpeechSynthesisErrorEventInit inherits from SpeechSynthesisEventInit:

dictionary SpeechSynthesisErrorEventInit : SpeechSynthesisEventInit {
    required SpeechSynthesisErrorCode error;
};