I've decided to switch to xhtml and I've added the following at the top
of my page:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
However, my page is still working and I can't see any warnings whenever
I use old html tags like <br> instead of <br/>. What other things
should I add to validate xhtml tags?