Beyond 1.0

XHTML 1.1

If you think of XHTML 1.0 as unwieldy, picky, and time-consuming, you'll fiind XHTML even more so. In our opinion, XHTML 1.1 is an example of the standards process taken to absurd levels, defining a standard that may be academically pure but is essentially unusable.

— Chuck Musciano & Bill Kennedy [source]

Modularization of XHTML

According to the W3C,

XHTML Modularization is a decomposition of XHTML 1.0, and by reference HTML 4, into a collection of abstract modules that provide specific types of functionality.... These modules may be combined with each other and with other modules to create XHTML subset and extension document types that qualify as members of the XHTML-family of document types.

[source]

Basically they're breaking XHTML up into component pieces — 28 pieces to be precise. You can pick and choose to create your own XHTML. What's the point? One idea is to allow document authors to economically deliver content on a greater number and diversity of platforms. A device (say a handheld computer) can be specified as using certain modules of XHTML rather than the whole set, greatly reducing the complexity of implementation on that platform.

XHTML Basic

This is an example of the aforementioned modularization. It may be thought of as XHTML for small information appliances.

According to the W3C,

the motivation for XHTML Basic is to provide an XHTML document type that can be shared across communities (e.g. desktop, TV, and mobile phones), and that is rich enough to be used for simple content authoring. New community-wide document types can be defined by extending XHTML Basic in such a way that XHTML Basic documents are in the set of valid documents of the new document type. Thus an XHTML Basic document can be presented on the maximum number of Web clients.

[source]

XHTML 2.0

This is not an official recommendation yet; it's still under development. It is radical, to say the least. It gets rid of h1 through h6. It gets rid of img. The br tag is also gone. It introduces a new model for forms.

According to the W3C,

Because earlier versions of HTML were special-purpose languages, it was necessary to ensure a level of backwards compatibility with new versions so that new documents would still be usable in older browsers. However, thanks to XML and stylesheets, such strict element-wise backwards compatibility is no longer necessary, since an XML-based browser, of which at the time of writing means more than 95% of browsers in use, can process new markup languages without having to be updated.

[source]

Opinions of this new effort are varied...

XHTML 2.0 seems to me the live proof that something is going wrong at W3C. I feel that this spec represents a solution maximizing the gap between authors' needs and industrial standardization compromise.

— Daniel Glazman [source]

As someone who writes web services for a living, XHTML 2.0 is everything I ever wanted.

— Jonas Jørgensen [source]