Mimic the effect of using recursive property substitution. E.g. this Ant setup code:

<macrodef name="substproperty">
    <attribute name="name"/>
    <attribute name="value"/>
    <sequential>
        <property name="@{name}" value="${@{value}}"/>
    </sequential>
</macrodef>
<property name="val-first" value="#1"/>
<property name="val-second" value="#2"/>
<property name="switch" value="first"/>
<substproperty name="derived" value="val-${switch}"/>

sets derived=#1. Would like something like this project.xml snippet to do the
same (assume /2 schema):

<property name="val-first">#1</>
<property name="val-second">#2</>
<property name="switch">first</>
<property-evaluate name="derived">val-${switch}</>

Alternately, just support nested substitutions even though Ant does not:

<property name="val-first">#1</>
<property name="val-second">#2</>
<property name="switch">first</>
<property name="derived">${val-${switch}}</>