def write_num_or_str_ref(tag, formula, data, type) # :nodoc:
      @writer.tag_elements(tag) do
        # Write the c:f element.
        write_series_formula(formula)
        if type == 'num'
          # Write the c:numCache element.
          write_num_cache(data)
        elsif type == 'str'
          # Write the c:strCache element.
          write_str_cache(data)
        end
      end
    end
def write_num_or_str_ref(tag, formula, data, type) # :nodoc:
      @writer.tag_elements(tag) do
        # Write the c:f element.
        write_series_formula(formula)
        if type == 'num'
          # Write the c:numCache element.
          write_num_cache(data)
        elsif type == 'str'
          # Write the c:strCache element.
          write_str_cache(data)
        end
      end
    end
Write the <c:numRef> or <c:strRef> element.