write_fielddata1_rank0 Function

   function write_fielddata1_rank0(self, data_name, x) result(error)
   !< Write `<DataArray... NumberOfTuples="..."...>...</DataArray>` tag (R8P).
   class(xml_writer_abstract), intent(inout) :: self      !< Writer.
   character(*),               intent(in)    :: data_name !< Data name.
   class(*),                   intent(in)    :: x         !< Data variable.
   integer(I4P)                              :: error     !< Error status.

   select type(x)
   type is(real(R8P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   type is(real(R4P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   type is(integer(I8P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   type is(integer(I4P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   type is(integer(I2P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   type is(integer(I1P))
      self%error = self%write_dataarray(data_name=data_name, x=[x], is_tuples=.true.)
   endselect
   error = self%error
   endfunction write_fielddata1_rank0