Function letterlike_encode 

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

Letterlike-symbols + circled-Latin selective substitution — replaces individual ASCII letters in the payload with codepoints from U+2100-214F and U+24B6-24E9 that NFKC-normalize back to the original ASCII letter. Unlike the math-*-encode functions which substitute every letter from a single block, this picks the most visually- distinct codepoint per letter to maximise WAF-rule mismatch while keeping the encoded string visibly identifiable.

The HackerNoon-documented ŚεℒℇℂƮ payload is essentially this function applied to the SQL keyword SELECT — backend’s NFKC casts it to SELECT and executes; the WAF’s signature regex sees an unrecognized codepoint sequence.