The PGN standard defines numeric annotation glyphs (NAGs) as a way to represent common annotation symbols in ASCII. The program does not support NAGs and does not handle them as valid PGN. The extension should recognize the glyphs and translate them to their unicode equivalent for display to the reader.
See 3rd game on https://en.wikipedia.beta.wmflabs.org/wiki/User:קיפודנחש1/ChessBrowser_test_cases