# File lib/vcard/vcard.rb, line 1162
      def birthday=(birthday)
        if !birthday.respond_to? :month
          raise ArgumentError, "birthday must be a date or time object."
        end
        delete_if { |l| l.name == "BDAY" }
        @card << ::Vcard::DirectoryInfo::Field.create( "BDAY", birthday );
      end