SubresourceType: "audio" | "document" | "embed" | "font" | "image" | "object" | "script" | "style" | "track" | "video"

A string indicating the type of subresource expected by a parent resource, e.g. 'image' or 'style'. Note this is not the same as a MIME type.

This corresponds to what is now called the ‘destination’ in the WHATWG fetch spec.