Note that much of the usage is probably in contexts will fallbacks where removal would do no harm at all, but this is a case where it's very hard to measure.

I'm somewhat hesitant to add this as @hsivonen has been working on a way to get rid of this entirely. By defaulting based on the TLD of the website and such. A default encoding that depends on the user's locale is rather terrible.

If the way the default encoding is determined changes, then presumably that should simply be reflected in this attribute.

@hsivonen, any thoughts on this? Do you think it would be harmful to expose the default encoding, merely useless, or something else?

I don't see legitimate use case for this. As a Web author, you should always use UTF-8 and declare that you are using UTF-8. At that point, what's the use case for knowing what the default would have been?

If someone tries to use it for something, what non-harmful uses it could have? I can think of a harmful use case: trying to guess what encoding to use for downloadable text files. (Correct way: Use UTF-8 BOM for downloadable text/plain and use Python, etc. -specific encoding declarations for downloadable scripts with #!.)

So I see this as useless and harmful if used, so I think we shouldn't spec this.

Can you tell if the Blink usage comes from "let's check everything" fingerprinting ad tech (not worth catering to)?

I don't know of any reason to use this API, my only concern is that it's supported in all engines except Gecko and usage is fairly high. Unfortunately, the use counter system can't answer interesting questions like "is this due to enumeration" or "is this always used with a fallback." I'll do a httparchive search to get some idea about how it's used in the wild.

I'm now attempting to deprecate and remove this in Blink.

It seems that was successful. \o/

Yep, I didn't hear about any fallout from that, sometimes it works out!