Function is_padding 

pub fn is_padding(c: char) -> bool

Whitespace for the opt-in CsvCellOptions::quote_whitespace_padded rule.

Deliberately NOT char::is_whitespace: that is Unicode White_Space, which includes U+0085 NEL and excludes U+FEFF, while JavaScript’s \s — which the TypeScript half uses — is the exact reverse. Left implicit, that asymmetry would be a silent cross-language behaviour split on two code points; spelled out here, tests/csv_cell_parity.rs sweeps it against the shared table.