Define a Choice field for Plone portal registry, with a vocabulary to choose from and a default value

registry.xml

<registry>

    <record name="some.record.identifier">
        <field type="plone.registry.field.Choice">
            <title>TheTitle</title>
            <description>TheDescription</description>
            <value_type type="plone.registry.field.TextLine" />
            <values purge="true">
               <element>choice 1</element>
               <element>choice 2</element>
               <element>choice 3</element>
            </values>
        </field>
        <value>choice 1</value>
    </record>

</registry>