public Appendable append(CharSequence csq, int start, int end) {reserve(end-start);for (int i=start; i<end; i++) {unsafeWrite(csq.charAt(i));}return this;}
public virtual OpenStringBuilder Append(ICharSequence csq, int startIndex, int length) {EnsureCapacity(length - startIndex);for (int i = startIndex; i < length; i++){UnsafeWrite(csq[i]);}return this;}