XML Schema - how to add "type=xs:string" into a complex element?

I got the following XML String:

<dyn_banner>
    <pattern>header.jpg</pattern>
    <param id='1'>attributes[123]</param>
    <param id='2'>attributes[456]</param>
.
.
.
 </dyn_banner>

This is what I managed to produce in XSD so far:

<xs:element name="dyn_banner">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="pattern" type="xs:string"/>
            <xs:element name="param" minOccurs="1" maxOccurs="unbounded"> 
                <xs:complexType>
                    <xs:attribute name="id" type="xs:integer"/>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
    </xs:complexType> 
</xs:element>

My problem now is that it's not clear for me how to tell the XML Schema that the element "param" does include a string (here: attributes[123 etc.].