@jgraham @gsnedders PTAL. We internally discussed what formats should be considered. I suggested we use the ones proposed here, but @OrKoN questioned whether they are compatible with other browsers. Considering implementations can throw unsupported operation, I think these should be okay.

Alternatively, we can make this a string and state it must be a image mime type. This is more flexible in case you folks have other requirements such as proprietary formats.

For example,

? format: string | browsingContext.ScreenshotFormat;
...

browsingContext.ScreenshotFormat = {
  type: string
} & Extensible

We could then change the algorithm to allow implementation-specific formats when the format is not one of the predefined types (webp, png, and jpeg).

I think if there will be no agreement that we need to support a shared set of the formats, we can probably have a vendor prefixed extension for the screenshot types in chromium-bidi.

@jrandolf please link and see comments on #383

@gsnedders @jgraham Is it ready to land?

@jrandolf are you going to add new wpt tests for this feature? CC @OrKoN.

Done: web-platform-tests/wpt#42804