I mentioned before that there are ways around the inability of elements to contain less-than signs or ampersands. That way is to use an entity reference . This is also useful for sample HTML - take a look at the source for this page. Most Web clients display pages in a proportional-width font, like Times or Helvetica. It's a block-level element, but its visual behavior is unpredictable.
Some Web clients indent it, some italicize it, some do both.
That's quite a bit more than the basics. For more information, start at the World-Wide Web Consortium . I recommend playing around with the concepts above. Just create a text file and change it around. Most Web clients can open a file on your computer.