php - How can I describe choice element using nusoap?

Question

I use nusoap to generate wsdl and I'm stuck at the point trying to describe choice element (xsd:choice).

The required xsd part looks like this:

<xsd:complexType name="sensitivityConditionType">
        <xsd:sequence>
            <xsd:choice minOccurs="1" maxOccurs="unbounded">
                <xsd:element name="sensitivityCondition" type="tns:sensitivityConditionType" minOccurs="1" maxOccurs="1" />
                <xsd:element name="operandCondition" type="tns:condition" minOccurs="1" maxOccurs="1" />
            </xsd:choice>
        </xsd:sequence>
        <xsd:attribute name="operator" type="xsd:string" use="required" />
        <xsd:attribute name="sensitivityType" type="xsd:string" use="optional" default="VIOLATELIMIT" />
</xsd:complexType>

The goal is that one of "sensitivityCondition" or "operandCondition" is required, but I didn't find any solution to produce this structure programatically.

Thanx for your help.