...

<field type="..." variable="...">
    <spec>
        ...
        <processor class="fully.qualified.ProcessorClassName" [backupVariable="..."]>
            <configuration>
                <param name="whatever-param-name" value="..."/>
                <param name="another-param2-name" value="..."/>
                ...
            </configuration>
        </processor>
    </spec>
    <validator class="fully.qualified.ValidatorClassName" txt="..." id="..."/>
</field>

The <configuration> section is optional.

For making migration easier, there can be used still <param name="..." value="..." /> entries instead or additionally to the newer <configuration> definition. This approach might be removed in one of the next major versions.

Parameter values may contain unresolved references to IzPack variables, which are resolved at installation time.

Attributes

• backupVariable (optional):
  a variable holding the original value entered by the user before processing took place
  This variable is not present before the processor action actually happens.

...