In a recent discussion someone put it that labels should be valid IDN U labels once they are "in the system". Now, when you make a DNS lookup the label you submit is "in the system". When it's on the side of a bus, to use the other extreme, it's not. Now, where do you draw the line for where "the system" starts? I don't think you can include all HTML documents or HTML mail message or any other place a URL can and does exist today.

Who knows?  There are standards for URLs, but if you look at three browsers you'll probably find at least four misinterpretations of them.

What I am arguing is that you cannot retroactively apply standards that haven't been followed; particularly for HTML you have a whole internet's worth of legacy data that any system must be able to handle and continue to do so for the indefinite future.

A./