syntaxdiagram specification: call for interested parties

One of my medium-term goals of late
has been to produce readable railroad-style SVG for rendering the syntaxdiagram
element.  I've got an implementation that I'm quite proud of, but
I don't know if it matches the official spec.  In fact, I don't know
if there *is* an official spec.  The element reference documents aren't
nearly detailed enough and the examples in them cover only simple cases,
not the edge cases I want to test.

I'd like to assemble a non-normative
explanatory document that explains syntaxdiagram to authors.  Does
anyone (a) want to help, or (b) know of any additional references that
I should look at first?

-- 

Deborah Pickett