<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:simpleType name="myDecimal">
<xsd:restriction base="xsd:decimal">
<xsd:totalDigits value="18"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:element name="foo">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="val" type="myDecimal" maxOccurs="unbounded"/>
<xsd:element name="ref" type="myDecimal" minOccurs="0"/>
</xsd:sequence>
</xsd:complexType>
<!--xsd:key name="myKey">
<xsd:selector xpath="val"/>
<xsd:field xpath="."/>
</xsd:key>
<xsd:keyref name="myKeyRef" refer="myKey">
<xsd:selector xpath="ref"/>
<xsd:field xpath="."/>
</xsd:keyref-->
</xsd:element>
</xsd:schema>