<?xml version="1.0" encoding="UTF-8"?>
<grammar
    xmlns="http://relaxng.org/ns/structure/1.0"
    xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
    datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">

<define name="pattern1">
    <data type="string">
        <param name="pattern">-?([0-9]+(\.[0-9]*)?|\.[0-9]+)</param>
    </data>
</define>

<start>
    <element name="elem1">
        <attribute name="attr1">
            <list>
                <ref name="pattern1"/>
            </list>
        </attribute>
    </element>
</start>

</grammar>