def write_pt(idx, value) # :nodoc:
      return unless value

      attributes = [ ['idx', idx] ]

      @writer.tag_elements('c:pt', attributes) { write_v(value) }
    end
def write_pt(idx, value) # :nodoc:
      return unless value

      attributes = [ ['idx', idx] ]

      @writer.tag_elements('c:pt', attributes) { write_v(value) }
    end
Write the <c:pt> element.