isJavaIdentifierPart
Returns true if this character (Unicode code point) may be part of a Java identifier as other than the first character.
inline fun Char.isJavaIdentifierPart(): Boolean(source)
fun main() {
val text = "abc_123$def 456"
val identifierChars = text.filter { it.isJavaIdentifierPart() }
println(identifierChars) // prints: abc_123def456
}