optional element in xml

how can i create xsd that describe optional element in xml. I know that if i have the following:

                        <xs:choice>
                              <xs:element ref="percent"/>
                                        <xs:element ref="name"/>
                        </xs:choice>
That means either i have xml with element percent or name. But how to make either percent or nothing?

i tried the following
                        <xs:choice>
                              <xs:element ref="percent"/>
                              <xs:sequence/>
                        </xs:choice>
and it does not work. any idea?Start Free Trial