request_field (OpenID::SReg::Request)

    # File lib/openid/extensions/sreg.rb, line 171
          def request_field(field_name, required=false, strict=false)
            OpenID::check_sreg_field_name(field_name)

            if strict
              if (@required + @optional).member? field_name
                raise ArgumentError, 'That field has already been requested'
              end
            else
              return if @required.member? field_name
              if @optional.member? field_name
                if required
                  @optional.delete field_name
                else
                  return
                end
              end
            end
            if required
              @required << field_name
            else
              @optional << field_name
            end
          end