I was reading an article about something we've all done at least once (written a web based forum), by using Perl and XML, where I came accross this quote:
In XML, it's traditional to use id as a unique identifier across all elements, regardless of type. That means having a thread with id="1" and a post with id="1" is forbidden. I want to keep the two separate, each with its own counting scheme, so I used different attributes.
That strikes me as being stupid. It seems like a hack to dodge some underlying problem with XML, or inherited tradition that pupports to make things easy by actually making things hard. After all, how do I guess if I'm using id or num to refer to my uniquue identifiers today?