code: func ToSSN(theString, delimiter string) (string, error) {
  	f := New(theString)
  	f.removeNonDigits()
  
  	if f.length != 9 {
  		return "", errors.New("string needs to be 9 digits for Social Security Numbers")
  	}
  
  	var buffer bytes.Buffer
  	count := 0
  
  	for _, i := range f.theString {
  		count++
  
  		buffer.WriteString(string(i))
  
  		if count == 3 || count == 5 {
  			buffer.WriteString(delimiter)
  		}
  	}
  	return buffer.String(), nil
  }
docs: // ToSSN will format the provided string as a SSN.