the current Transformation instance being executed. Useful for Macros which need to perform other
transformations in turn such as the Include macro which needs to execute the transformation if the
included page should be executed in its own context.
an id representing the transformation being evaluated. It's a free form name that may be used to perform
some caching based on a key. For example the Velocity Macro is using this id to pass it to the underlying
Velocity Engine so that it caches macros using this key.