Mark, I’m really not sure how this might work, I was mostly hoping Tinderbox had the magic already to read my mind (it has been so useful in my other efforts at qualitative analysis and typically there as already been a feature that I can appropriate). 
@PaulWalters example is pretty cool–I especially like the outline tab where you can see via check marks which codes are applied to any note. This is similar to a view I sometimes try to use in Excel.
Ultimately, I guess I was imagining there could be some kind of dot operator for “collect” or “list” that would produce a record of co-occurences across set/list values. So, user would write an collect expression like so:
collect.cooccur(children(/QualData),$OpenCodes)
which would return this text:
blue;green, 4
red; blue, 2
blue;orange, 2
Now that I write this, I see this is pretty different from the way most Tinderbox operators work in terms of returning values, but it doesn’t seem completely out of the realm of possibility (from my user perspective at least–I have no idea what technical issues might prevent such an example).
Given this list, I could then choose to make agents to see the exact notes where they occur, or turn the values into some kind of set to view in Attribute browser or something.
I’m sorry Mark B, I know this is pretty half-baked! This is the first time I’ve really been trying to accomplish this kind of analysis and Tinderbox is the first place I looked. After I have some mySQL experience trying to do the same thing, I might have better ideas of what I’m looking for and how it could be implemented in TBX.