The data layering feature previously proposed has been implemented in Daffodil.

There were minor changes from prior Wiki description. The wiki page is updated to reflect what the implementation actually does. The examples on the wiki page actually run and have been incorporated into Daffodil regression tests.

This feature is also being successfully used to create iCalendar and IMF format DFDL schemas. Those are not yet released for public consumption, but the feature is being successfully used for "real" formats and is thusfar, working as designed.

Of the changes since prior draft of the design note, We changed a property value name. Property dfdl:layerLengthKind='boundaryMark' was done to replace the 'terminator' property value to avoid confusion with ordinary dfdl:terminator property.

Thusfar we've not run into a need for a more general mechanism for passing parameters from the schema to the layering. The boundary mark, and the length have been sufficient, but this feels like an area where something more general may be needed in the future. For example, there are really 3 different kinds of layerings all known as "base64". Rather than having one general "base64" with a parameter, we're currently requiring that each variant have its own layering transform name, e.g., "base64_MIME" is one of them (the only one implemented thusfar).

...mikeb