HTML and XHTML

XHTML is really just a newer version of HTML. The X stands for extendable, which allows new tags to be defined. XHTML also has stricter rules for coding pages. Here are the major restrictions:

All tags should be in lower-case.
All tags must be closed (either with a closing tag or ending the tag with "/>"
Attribute values must be in quotes.
XHTML tags must be properly nested.
The DOCTYPE should be specified at the beginning of the document. This declaration is recommended for our class:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

HTML 5

While it hasn't been officially adopted yet, many browsers are starting to support HTML 5, the next version of HTML. It supports a variety of new tags (e.g. footer, article, section, nav) for indicating logical elements on a page. It is also less strict than XHTML and has a simplified Doc Type declaration: <!DOCTYPE html>

For our class projects, follow the XHTML guidelines, which will continue to work with HTML 5.