It's just oxalates, there shouldn't be too much of it in their diet because it interacts with the way they rid themself of calcium, but I wouldn't call it "very toxic" when getting to it once in such amounts. It is toxic to sheep and horses though, but even there it's only when a lot of it is growing on the meadow.
Rabbits are one of the most resiliant creatures regarding plant toxins I know of, either they can stomach what kills other animals, or they know how much they can stomach (and apparently use some for self medication), or they don't eat it at all. Unfortunatly most of those lists are not considering this, if something is toxic for one animal, it's toxic, period.
Most real problems occur with rabbits that are not used to green forage and decorative plants, some of those really pose dangers.
I do not regard oxalets as imminent thread either, the problem mentioned about dock seeds (which I doubt about) was not oxalates, but potassium binoxalate which occurs as a result of reaction between potassium hydroxide and oxalic acid. This is at least what they claim. Nothing happened, my bunnies are fine.
I'm suffering from tendinitis for the last 7 months, fingers and arms, and oxalates are one of the main substances that I should avoid. The problem is I do love the taste of oxalates and forage specifically some plants that have very high oxalate content and sour oxalate taste such as Oxalis corniculata and Oxalis debilis. These are the oxalis from my area, all my life I have never taste anything better than this plant.
Unfortunately I had to stop eating this heavenly plant after tendinitis. Oxalate content in Oxalis plant is much more than in docks, even the name oxalate derives from the plant's name Oxalis, which means sour in Greek.
As for the docks, I kept eating docks if they are fresh and low in oxalates, anyone can guess the oxalate content by tasting it. Fresh leaves low in oxalates and older leaves high. It also depends on the species, there are 5 Rumex species in my area, most commons are Rumex crispus and Rumex pulcher. I eat and fed my rabbits (rarely) only one variety of Rumex crispus which taste literally no oxalate when eaten fresh.
This is the Rumex crispus variety that I sometimes fed to my rabbits, it slightly differs from the other crispus varieties, slightly resembles to Rumex pulcher.
And this is one of the docks that I always avoid, tastes very sour, Rumex obtusifolius.
I do believe that oxalate content might completely differs according to area, climate, variety etc. For me the general rule is the older and sourer has high oxalate and vice versa.
