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| Expressions are in the form of `${key:defaultValue}`. If the key is prefixed with `sys.` a system property is used. If the key is prefixed with `env.` an environment variable is used. In all other cases the properties are resolved from the `org.jboss.logging.tools.expressionProperties` path. If the key is not found in the properties the default value will be used.

| Expressions are processed at compile time. The values will be hard-coded in the generated source files.