Well, the problem here is that the item descriptions are programming language-agnostic.
Mozilla (or, more specifically, the Mozilla Developer Network) contains documentation for JavaScript arrays only. The same description will be shown independent of the programming language you’re using, which makes little sense when you are coding in Python or Lua. There’s a related bug ticket.
Another issue is that links inside descriptions seem to be not reachable (at least in desktop computers), as the description will be closed immediately after the cursor leaves the item they are describing. I’ve reported this issue here.
Anyway, for the time being, you can search on Google to find the relevant documentation for your programming language. Here’s the Lua Arrays documentation.