The new support for media types in TURF from URF-91, along with more research on the Jekyll et. al. "front matter" delimiter --- for placing YAML at the top of a Markdown document, provides us an opportunity to overhaul and improve the TURF approach to defining namespaces and create a better signature at the same time.
The new TURF signature will be ===>urf<.
The >urf< will be a standard TURF media type literal, except:
If the primary type is text, the text/ should be left off.
A description block :…; is allowed immediately after the media type itself, inside the >< delimiters, in which to define namespaces as properties as per URF-53.
This allows a signature that corresponds to similar modern "dividers" such as "front matter", but allows future versions of the specification to allow a document to incorporate even different types of content, or at least signal some transition. Lastly the namespace declaration under this approach is still clearly outside of the document proper, as it is "inside" the media type literal, which is really not a media type literal value but part of the signature.