I knew Ralph had said this, but only just stumbled across where he wrote it
down.
It was when Netscape submitted the XML-ified version of Guha's MCF to W3C,
June 1997. This work was picked up by the RDF Model and Syntax WG. To put
this in context, this was before the XML spec was itself finalized.
https://www.w3.org/Submission/1997/8/Comment.html
"An important requirement on the metadata framework is that parsers must be
able to produce a parse tree of the metadata without the assistance of an
auxiliary format description. This corresponds to the XML *well-formed*
criterion"
I share this since various of us have been banging on about this design
issue on the Signed LD thread, w.r.t. JSON-LD Contexts.
RDF/XML took the verbose path, such that knowing only the bytes in the
file + base URI, you could get the same triples out, with no extra info.
It's neither better nor worse than other approaches, but it is a
distinctive design constraint and I'm glad I found it written down
somewhere, finally. Turtle, Ntriples, also work the same way; GRDDL, CSVW
RDF mappings don't, as they require multiple files before you know what
triples you'll get.
Dan