One of the trickiest aspects of designing valid and usable Web pages is making sure that when you nest tags within one another the nesting is legal. If you nest on tag inside of another when you're not supposed to some browsers may mangle the final display. If you don't nest tags properly -- list items inside of lists containers or table data cells inside of table rows for example -- browsers may also mangle the final display.
To make your Web page development easier LANWrights expert programmer Bill Brogden designed an HTML context applet that you can use to find out which tags you can nest within which others. The applet includes information from the strict HTML DTD as well as the loose. To find out what other tags an individual tag can hold choose the DTD you'd like to work from, select the tag you want to know more about, and click the "can contain" radio button. To find out what other tags an individual tag can be nested within click the "can be contained in" radio button. Nothing could be easier.
Note: You must have a Java enabled browser with Java turned on in order to use this tool.
E-mail: HTML 4 For Dummies, 2nd Edition