>Always wondered that...
Well, that is standard HTML code. If you want to see some other HTML code that people use in messages, you can press "Reply" in any message that uses a special effect you like (as long as you don't press "Send", you can cancel the message - just close the window, click on another message in the top pane, or click on the "Back" button of your browser). For example,
bold or
italic.
Some HTML codes are not allowed in the UT, for security reasons.
Some changes to messages are done automatically by the UT (for example, expanding common acronyms, adding hyperlinks to key words).
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)