appendRange
Appends a subsequence of the specified character sequence value to this Appendable and returns this instance.
@IgnorableReturnValuefun <T : Appendable> T.appendRange(value: CharSequence, startIndex: Int, endIndex: Int): T(source)
fun main() {
val sb = StringBuilder()
val source = "Hello, World!"
sb.appendRange(source, 7, 12) // appends "World"
println(sb) // prints "World"
}