PerlMonks engine automatically replaces all symbols not representable in ASCII by their HTML entity codes

Nit: It's actually the browser doing that, and it's for characters outside of cp1252 (not ASCII).

PerlMonks pages are returned as cp1252, so the browser knows that forms must be submitted using cp1252. Characters outside of cp1252 (e.g. "ы") can't be submitted, but rather than throwing an error if such characters are provided, the browser provides an HTML encoding of the character (e.g. "ы") instead just in case that works. Of course, it doesn't work within code tags because PerlMonks escapes "&" in code tags so that it shows up as "&".