Funciton (186 bytes in UTF-16)

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This program prints “world”.

Any substring you remove from this will stop it from being a complete box, which the parser will complain about — with only one exception: removing the entire middle line, leaving this:

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Doing so removes the dangling end on the right (the output). This is no longer a valid program. It is simply an empty comment, but the parser expects a program with exactly one output:

Error: Source files do not contain a program (program must have an output).

Therefore, this program is pristine.