Elad Alon

> It is interesting how things that relate to either audio or video are instead added at the options e.g. systemAudio, instead of being added as a media track constraint....

> I think displaySurface is an odd case. Because it merely suggests which surface is to be displayed, it does not have the effect of a constraint. However it is...

> Feature detection can be used for these preferences, for instance https://jsfiddle.net/vayrLp85/ is using the fact getDisplayMedia should reject with InvalidStateError outside of a user gesture in Safari. Thanks for...

Thanks for answering the "how?" Could you please answer "why?"

~(Btw, it's not "100% reliable". For instance, it requires a transient activation. What if the app wants to feature-detect on load, before deciding which UX to show to the user?)~...

> If an API can be done in JavaScript in a simple manner, as is the case here, why should the UA bother to implement it? 1. This is not...

> Regarding "why", the bar for custom feature detection APIs should be extremely high IMHO, because it's a problem that disappears over time. [This problem will NOT disappear over time](https://github.com/WebKit/standards-positions/issues/6):...

> It seems no worse than the MDN example I gave. ~You linked to multiple pages. The MDN one has 16 pages. Could you please be more specific?~ (Edited) ~Examining...

Sounds reasonable.

If it's not Web-exposed, could it be used in the IDL files of UA implementations without being reflected by a spec change, perhaps?