It used to be that people placed hidden text all over their pages to manipulate search engines. Today, people are finding creative ways to make hidden text that’s intended for human eyes.

To prevent spoilers on IMDb, the plot keywords are hidden until you hover over them with the mouse. A bit if JavaScript changes the CSS class on mouse over.

Some forums hide spoilers by making the text the same color as the background. To read the otherwise invisible text, you just select it with your mouse.

A friend of mine uses the ACRONYM tag to provide snarky inline commentary on his blog. In some browsers, a dotted underscore reveals the location of the hidden text.

The webcomic xkcd always hides a second punchline as a mouse-over tooltip. Some people use ALT for this because IE allows it, but TITLE is preferred.

All the mouse rollover techniques break down on the iPhone and other mobile platforms. If anyone can come up with an easy way to see the xkcd tooltip in MobileSafari, please comment. (I’m looking at you, Google Reader mobile developers!)

Sometimes people put cute messages in HTML comments or even more obscure places. The geek forum Slashdot stashes a Futurama quote in the HTTP headers of each page. I have to wonder how long that was there before someone noticed.

Hidden text isn’t just for Easter eggs and secret messages. Some uses are more functional. As a programmer I sometimes hide debugging messages in a page. I know it’s there but most readers won’t be bothered by it.

In some cases, hidden text is meant to be revealed to certain readers. NOSCRIPT blocks were once considered critical to assist people with JavaScript-deficient browsers.

Visit the homepage of Daily Kos with ad blocker enabled and you’ll see a message imploring you to subscribe or at least allow them to show you ads. How does it work? The text is normally hidden by CSS in a file called adblocker.blogads.css. The ad blocker thanks that file name is probably an ad, so it eliminates the CSS that would hide the message. Clever!

Any other ways to hide text in plain sites?