Contra sibling comments, it technically isn't a legal requirement. It's entirely voluntary, a memorandum of understanding between manufacturers, facilitated by the EU.
Obviously 'voluntary' here deserves some scare quotes since the EU had made it very clear that it was willing to swing its sledgehammer and formally regulate if the manufacturers couldn't agree on a standard amongst themselves. Which would have been less good for everyone (including the EU), e.g. since formal legal regulations are a lot harder to change with the times, So they were pretty incentivized to work something out, and happily they did.