I've brought up an idea a couple of times here: If (quasiquote ...) and (unquote ...) match up and nest like parentheses, then what if we generalize that analogy to higher dimensions?
After years of going back to the drawing board over and over, I finally have a working, reasonably elegant (if slow), and most importantly, documented implementation of hypersnippets and hyperbrackets in Punctaffy. I'm really excited to be able to give examples of how these can be used for things other than quasiquotation.
The "Introduction to Punctaffy" section introduces the idea of degree-2 hyperbrackets. There are precious few examples where degree-3 hyperbrackets would come in handy (much less higher-degree ones), but the infrastructure is working for those as well.
There are still a number of directions I hope Punctaffy will take from here, but it's finally past the "sorry, I haven't written up good documentation, so I don't know how to explain" stage that it's been stuck in for quite a while. :) If you're interested, I've written up some in-depth discussion of those future ideas in the "Potential Applications" sections. One of those (the interaction between 'unsyntax and ellipses in the Racket syntax template DSL) would even be a practical application of degree-3 hyperbrackets.
This documentation totals to something like 30,000 words. Most of those words are the reference documentation of Punctaffy's hypersnippet-shaped data structures (hypertees and hypernests). Don't worry about reading through all of it, but I'd be very happy to see if anyone could make it through the introduction. After 4 years of not having much to show people, I really hope that introduction will help. :)