isDefined

Returns true if this character (Unicode code point) is defined in Unicode.

expect fun Char.isDefined(): Boolean(source)

fun main() {
    val definedChar = 'ℑ'          // Greek letter Iota
    val undefinedChar = '\uFFFF'   // Undefined Unicode code point

    println("Is '${definedChar}' defined? ${definedChar.isDefined()}")   // true
    println("Is '\\uFFFF' defined? ${undefinedChar.isDefined()}")        // false
}

Source