And here's the answer to the sibling asking why it's a problem, since they mean exactly the same on practice :)
What it literally means and what people understand when reading it aren't the same thing. On this case, for people creating sites, "up to" leads immediately into the real meaning of the phrase, while "at least" strongly implies the opposite. But for people creating browsers, the implication is inverted.
What it literally means and what people understand when reading it aren't the same thing. On this case, for people creating sites, "up to" leads immediately into the real meaning of the phrase, while "at least" strongly implies the opposite. But for people creating browsers, the implication is inverted.