Provide some guidance on creating new list types

[marcoscaceres]

I noticed that the Web Speech API is defining new *List and list-like types:

• SpeechRecognitionResult
• SpeechRecognitionResultList
• And more...

They are "array/list-like" in that they have a .length, an index accessor, and so on, but are actually incompatible with the ES iterator protocol (and violate the "give things constructors principle").

We should probably provide guidance against defining new list types for the platform, and instead rely on WebIDL iterable (or setlike, tho that's rare I believe).

[annevk]

Is this perhaps because it's an old API in a way? I think for new stuff we generally encourage sequence<T>.

[marcoscaceres]

Sure, it’s more to catch APIs developed in isolation (in the off chance they also land at this guide). We can’t keep an eye on everything, unfortunately.

[hober]

See also WICG/construct-stylesheets#45

[hober]

See also #50.