How does @visible work?

[sub]

Yes but my comment is both ["@variableIsTrueOrFalse"] and ["!@variableIsTrueOrFalse"] appear to return true if it is null. I think the first one should return false.

I understand where you're coming from, but it was a conscious decision to make things visible if the variable was present, since in most cases it'd be because of a typo or bug in the plugin. It'd probably break things to change it too, after having always done it this way in NPVR (and GBPVR before it).