XML arguably isn’t plain text, but a binary format: If you add/change the encoding declaration on the first line, the remaining bytes will be interpreted differently. Unless you process it as a function of its declared (or auto-detected, see below) encoding, you have to treat it as a binary file.

In the absence of an encoding declaration, the encoding is in some cases detected automatically based on the first four bytes: https://www.w3.org/TR/xml/#sec-guessing-no-ext-info Again, that means that XML is a binary format.

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