What is "v" in this context? And why does any old number not just work?

Game Dev Tycoon modding
#1

In this example from the wiki,

GDT.addResearchItem(
    {
        id: "Swift Loading",
        name: "Swift loading".localize(),
        v: 4,
        canResearch: function (company) {
            return LevelCalculator.getMissionLevel('Level Design') > 5 //The 'Level Design' level has to 6 or higher
        },
        category: "Level Design",
        categoryDisplayName: "Level Design".localize()
    });

What does v: 4 mean, and why does any old number not work?

#2

I moved 15 posts to an existing topic: Official Mod Code Error Thread - For Mod Authors

#3
Official Mod Code Error Thread - For Mod Authors