XHTML Basic 1.1 is the evolution of XHTML Basic. It adds some important features, but is not a revolution, as you might expect.

XHTML Basic 1.1 is also a step towards unification between “desktop and mobile” markups. XHTML-MP was developed based on XHTML Basic, adding WCSS [PDF] and some tags and attributes particularly important to the mobile space. With XHTML Basic 1.1, the OMA and the W3C have worked together to bring them together.

For these reasons, if a browser already supports XHTML-MP will support most features of XHTML Basic 1.1.

Read more: What is XHTML-MP?

If you are developing for the mobile, XHTML-MP is the way to go as it is the most widely supported markup in modern devices. We can consider WML legacy. If you are really forward looking and maybe thinking of using a single markup for your “desktop” layout and mobile layout, then XHTML Basic 1.1 might be your choice. Support of new tags may vary. The good news is that differently from WAP 1 days, most devices will ignore unknown or unsupported tags and not just choke.