public void Insert(int index, char c)
{
stringBuilder.Insert(index, c);
OnChange?.Invoke(FullString);
OnInsertChar?.Invoke(index, c);
OnInsertString?.Invoke(index, c.ToString());
}
public void Append(char chr)
{
int index = stringBuilder.Length;
int l = Length;
stringBuilder.Append(chr);
InvalidateCache();
OnChange?.Invoke(FullString);
OnInsertChar?.Invoke(index, chr);
OnInsertString?.Invoke(index, chr.ToString());
}