When defining a installer, some of the configuration is evaluated during install. So you can use variables for this attributes.
Other attributes are evaluated during compile. The dynamic variables can not be used at this stage, because they can evaluated only during install. But the static variables are available during compile also and could be useful for customized builds.
Some attributes did accept static variables since 2010, others were added within IZPACK-1234.
There still may be attributes were static variables would be useful. It could be a reasonable idea to resolve static variables in the XML-parser, so that variables could be used in all definitions without special handling on the sprecific attribute.
Any comments on this?