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>