insert method
Implementation
BidiRope insert(int index, String text) {
if (index < 0 || index > length) {
throw RangeError.range(index, 0, length, 'index');
}
if (text.isEmpty) {
return this;
}
final newRope = _rope.insert(index, text);
final newText = newRope.toString();
final containsRtl = BidirectionalText.containsRtl(newText);
return BidiRope._(newRope, containsRtl);
}