HTML Type

Because HTML is an evolving specification, with new features being added and old ones obsoleted, the browser needs to know exactly what dialect of HTML it should be using when trying to render a particular page. To allow this, every web page needs to include a declaration of the HTML type.

Historical Perspective

If you look at the source, you will see that the type definition for this page is:

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

So, what does this rather complex line of code mean? Firstly, it says that the basic DOCTYPE is html. Then, specifically, that the exact version of HTML that is being used is XHTML version 1.0 Transitional and the complete definition for this form of HTML can be found at the given URL.

The inclusion of the URL tells you were to find the DTD (Document Type Definition) for the version of HTML. This is needed because XHTML is really a form of SGML (Standard Generalized Markup Language). XHTML is an extended version of HTML and version 1.0 became the recommended format for web pages in 2000. Although this recommendation was superceeded in 2001 by version 1.1, this is not actively used by most web designers as it is not auotmatically supported by many web servers.

The Transitional part of the type declaration means that some features of the older version of HTML, which are not allowed in strict XHTML, will actually continue to work. In particular the "target" propery for links is supported.

The complete range of type declarations that Dreamweaver CS6 supports are:

For CS4, released in 2008, the list is the same but without the HTML 5 option.

HTML 5

The current version of HTML being supported and developed is HTML 5, so I suggest that you use that version to develop your own pages. The type declaration for an HTML 5 document is very simple:

<!DOCTYPE html>

This is greatly simplified because HTML 5 is not based on SGML and so it does not need a DTD.

However, do remember that a range of older HTML elements are no longer supported in HTML 5. These include the font tag and all the frame related tags.

For a complete list of deprecated tags, check out the HTML 5 site.

Links

You can find a good discussion of the doctype declaration, along with a range of examples, on the W3Schools site.