Is it possible to conceal #BEGIN/END?

[madeupandprobablydoesnotexist]

This seems possible with emacs via hiding emphasis markers (?)
https://reddit.com/r/emacs/comments/1e03roh/orgmode_hide_special_characterslines_for_better/
But when using this in nvim, it does hide the typical markdown characters, but not the BEGIN/END parts of a src block. I'm not sure if I'm missing something but I've spent quite a while trying to search through the help to no avail.

[madeupandprobablydoesnotexist]

Also, how do we add missing language syntax highlighting? e.g. PL/1 is in nvim by default but not an option for src blocks.