Function sharp_s_encode 

pub fn sharp_s_encode(payload: &str) -> String

Sharp-s (ß U+00DF) substitution for s/S.

ß lowercases to itself in most locales, but Unicode FULL case-fold (str::to_lowercase in Rust, str.casefold() in Python) maps the CAPITAL letter sharp s ẞ (U+1E9E) to ss. WAFs that case-fold before regex see different byte sequence; backends with full Unicode casefold reach the same script / select. Narrower applicability than turkish_i_encode.