docs: def _internal_add(self, other):
          """ Used for specifing addition methods for
             __add__, __iadd__, __radd__
          """
          if hasattr(other, "datatype"):
              if other.datatype == self.datatype:
                  rtn_val = self.value + other.value
              else:
                  rtn_val = self.value + int(other.value)
          else:
              rtn_val = self.value + other
          return XsdInteger(rtn_val)