Indicate that thing needs user action to work

[marcoscaceres]

There are things in the platform that can only succeed because of some user action. For example, directly calling:

document.body.requestFullscreen();

In Gecko, results in the following warning:

⚠️  Request for fullscreen was denied because Element.requestFullscreen() 
was not called from inside a short running user-generated event handler.

Would it be useful to have some means of annotating such behavior using WebIDL?

[domenic]

I think this would be reasonable if it would be something bindings generators could use to generate generic code. I'm not sure if that is the case; we'd want to do an audit of existing platform uses of triggered by user activation.

If we did, we would probably define it as an extended attribute in HTML, since HTML is what defines triggered by user activation.