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wtf8
WTF-8 is a superset of UTF-8 that allows unpaired surrogates.
From ES6 6.1.4, "The String Type":
If we try to encode these ill-formed code units into UTF-8, we similarly get ill-formed UTF-8. WTF-8 is a fun name for that encoding.
https://simonsapin.github.io/wtf-8/