StartIndex cannot be less than zero.

[LeoJHarris]

Hi great work on this plugin, just a suggestion to possibly append a decimal point if it didn't happen to be there to catch index out of range exceptions:

 string number = behavior.Text.ToString();

            if (!number.Contains("."))
            {
                number += ".00";
            }

            string decimalValue = number.Substring(number.IndexOf("."));
            FormattedString fs = new FormattedString();