Considering only the copy-to-clipboard feature I feel like the ```lang,copy/```lang,nocopy syntax is preferable because it has some chance of being understood by other tools.
That said, as we add more configuration to these code blocks there might be a point where the aggregate of that configuration starts tipping the scale in the other direction. The main constraint that I can see with the ```lang,copy/```lang,nocopy syntax is that all the configuration has to fit on one line.
This thread also mentions configuration to display line numbers as a potential future code block feature like this and the in-progress PR also mentions configurable line wrapping and line highlights as two more potential future code block features.
For basic boolean configuration we can use comma separated list of labels but if there’s configuration that requires a value (or a list of values) then the syntax quickly becomes more complicated and the risk for typos or invalid configuration increases.
As long as we treat is as an experimental (that is, not necessarily stable) feature and reserve the right to change our mind as more of these related features are developed and get a chance to reevaluate the aggregate syntax before marking them as non-experimental I don’t see any problems with going with the the ```lang,copy/```lang,nocopy syntax for now.