HTML and CSS Reference
In-Depth Information
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
In the short run, it doesn't matter which you pick. In the long run, you'll probably want to migrate your
documents to the strict DTD, but for now you can use the frameset DTD on any pages that contain frames and
the transitional DTD for other documents.
Browsers look at the public identifier to determine what flavor of HTML they're dealing with. However, they will
not actually load the DTD from the specified URL. In essence, they already know what's there and don't need to
load it every time.
Other, non-HTML-specific tools such as XSLT processors may indeed load the DTD. In this case, you may wish to
replace the remote URLs with local copies. For example:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"dtd/xhtml1-strict.dtd">
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"dtd/xhtml1-transitional.dtd">
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"dtd/xhtml1-frameset.dtd">
As long as the public identifiers are the same, the browsers will still recognize these.
Some documents on a site may already have DOCTYPE declarations, either XHTML or otherwise. Many tools
have added these by default over the years, even though browsers never paid much attention to them. Thus,
the first step is to find out what you've already got. Do a multifile search for
<!DOCTYPE
. Unless you're writing
HTML or XML tutorials, any hits you get are almost certain to be preexisting DOCTYPE declarations. In most
cases, though, they will not be the right one. Usually, there are only a few variants, so you can do a constant
string multifile search and replace to upgrade to the newer XHTML DOCTYPE. Any that don't fit the pattern can
be fixed by hand.
Documents that don't have a DOCTYPE are also easy to fix. The DOCTYPE always goes immediately before the
<html>
start-tag. Thus, all you have to do is search for
<html\w
and replace it with the following:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"dtd/xhtml1-strict.dtd">
<html
You should also take this opportunity to configure your authoring tools to specify the XHTML DOCTYPE by
default. Often it's a simple checkbox in a preference pane somewhere.
$ tidy -asxhtml --doctype strict file.htmlTagSoup does not add DOCTYPE
declarations. You'll need to insert these by hand. Tidy adds a
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