OpenStreetMap doesn’t allow multiple tags with the same tag key. But there is a believe out there in OSM land, that you can work around this by putting all the tag values you want into one tag using semicolons as separator characters. So if there is a bank with an ATM machine, people tag [amenity=bank;atm]. Or there is a road with several refs, then they tag them as [ref=I 70;US 40] and hope that it will magically work. And it does work in some cases. But in many cases it doesn’t. Let’s look into this a bit.