[html] How to make HTML code inactive with comments

Behold HTML comments:

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http://www.w3.org/TR/html401/intro/sgmltut.html#idx-HTML

The proper way to delete code without deleting it, of course, is to use version control, which enables you to resurrect old code from the past. Don't get into the habit of accumulating commented-out code in your pages, it's no fun. :)