Short answer:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML
4.01//EN" "
http://www.w3.org/TR/html4/strict.dtd">
That is a doctype for HTML 4.01 Transitional, a standard
for programming webpages. It goes before the <html> tag.
Should you add one? Only if you are going to follow the
specifications for creating webpages that comply to the
W3C's standards (
www.w3.org). If you're using Frontpage,
you can add one if you want, but it's likely it will not
validate as Frontpage does not "absolutely" conform to
the standards as far as I know. It's not terrible though,
but not perfect.
Long answer:
Doctypes are lines added before the <html> tag to
identify your document as conforming to a set of W3C
standards for webpage programming. The major players in
the industry, software companies, designers etc come
together to create the standards. If you adhere to
standards, it makes life easier for everybody. Examples:
your pages are more likely to look the same in any
browser, and will be easier to update later if standards
are applied. As well, standards open the door to the
internet for people of all ages, races, languages, as
each browser will handle the webpage the same way as the
next one. Think of it like this, you expect cars 20 years
ago to operate on the same principles that apply to them
today, right? You can fix an old car just as easily as a
new one, since they basically are still the same
underneath. And somebody who speaks Russian can still fix
my car, even though I speak English. Why shouldn't the
web operate like that?
Generally, the ones you will see most are HTML 4.1 and
XHTML versions 1.0 and 1.1. The main difference between
HTML and XHTML are that no empty tags are allowed, <br>
in HTML 4.1 must be <br /> in XHTML 1.0. XHTML is new
standard that seeks to get rid of the data portion of
HTML, and concentrate more on the presentational aspect
of webpages. Use XHTML in combination with CSS (Cascading
Style Sheets).
If you want to learn more, check out these sites:
http://www.w3.org
http://www.w3schools.com <- One of the best sites ever,
and free!
-Duncan
