Creates a properties file with the effective values of some user-defined expressions. Unlike Maven's built-in expression syntax for interpolation, these expressions use forward slashes to navigate down the object graph and support access to individual collection/array elements. Furthermore, the result of an expression need not be a scalar value but can also be a collection/array or a bean-like object (from the Maven model). For example, the expression "project/dependencies/0" would extract the first project dependency. In more detail, this example expression could output the following keys to the properties file: Expressions that reference non-existing objects or use invalid collection/array indices silently resolve to null. For collections and arrays, the special index "*" can be used to iterate all elements.