This concept, ,which has been discussed before, is in high demand in the Daffodil user community to enable DFDL to be used to parse image file formats.

The use case is to provide uniform image-metadata access without getting bogged down in the large byte-array that makes up most of the file and would be very large (and pointless) if rendered into XML or JSON.

So our proposal, (which will get turned into an official Experimental feature document), has been simplified and revised and is described here: