Please don’t take this as a feature request, because it’s coming from me — currently I’m not a user — but you know how you can select parts of the data in interactive graphs? https://vega.github.io/vega-lite/examples/interactive_brush.html I think it would be amazing if you could somehow def the selected part of the data so that you examine it in more detail in the REPL.

But as I said, I’m planning to use Oz, but I haven’t

Thanks for the suggestion! And not to worry suggesting a feature having not used it; Knowing what folks who haven't used it would be interested in is just as important to me as from those who have. This will more or less be possible soon as a result of https://github.com/metasoarous/oz/issues/13 & https://github.com/metasoarous/oz/issues/69. But I could see adding some functionality which would make the particular task you're describing more ergonomic. Please feel free to add a thumbsup on those issues or submit a more specific issue. And again, thanks for the feedback!