Full Unicode uppercase expansion for c as a String. Returns the empty string when c has no multi-codepoint expansion — pair with hasUppercaseExpansion (or call toUppercase instead) to avoid the scan when you only need the single-codepoint form.

Examples

uppercaseExpansion('ß') // "SS" uppercaseExpansion('fi') // "FI" uppercaseExpansion('a') // "" (use toUppercase for 'A')