So what’s up with the little grey button at the bottom of this site? It is my official Invalidation Badge. It’s mere presence on every page of this site renders my entire domain XHTML 1.0 Non-Compliant. Invalid. Erroneous. Whatever you want to call it. Here are the various crimes this one line of code commits:
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By invalidating my entire site with this one line of code, I ensure that I am made aware the instant it matters. The instant this stuff starts to break anything in the real world, I will know. If I only had a few small errors on a few random pages around my site, I could easily miss the day when “the big switchover” happens and wind up with broken pages I don’t know about. And since this code is in the form of a server-side include, I can freely remove it with a few clicks.

It’s kind of like carrying a canary down a mine shaft with you. As long as the canary is alive and chirping, you know you’re okay for air. Actually, I guess it’s not really like that.

Clever.