XHTML & HTML5
Extensible Hypertext Markup Language (XHTML) is an XML-based markup language which extends standard HTML. XHTML is an application of XML and therefore has full XML features and capabilites including being parsed by standard XML parsers. This gives XHTML the advantage of be available to many more uses and applications than just desktop web browsers.
All our non-mobile sites are XHTML and CSS based. XHTML 1.0 has been a W3C (Word Wide Web Consortium) Recommendation since 2000. Because we work closely with many XML formats and really like the portability of it, We're very interested and keeping a close eye on the development of XHTML5, which will emerge as part of the HTML5 specification.
HTML 5 (HyperText Markup Language Version 5) is the proposed next standard for XHTML 1.0. We're particularly interested in it as it has already been allowing us to build Rich Internet Applications (RIA)s without the need for proprietary plugins such as Adobe Flash and Sun JavaFX. HTML5 provides a native graphics/animation canvas and other contextual tags that help define headers footers and menus and cool features for working offline.
While we started dabbling with HTML5 and CSS 3 as soon as Safari and Firefox offered partial support for it, WebKit supported mobile browsers offer HTML5 support that has enabled us to create web applications specifically for phones and mobile platforms and look work and feel like native phone apps.
WebKit and other HTML5 browsers
We love mobile development, while we can create full apps using the iPhone SDK and Android SDK, we find that after speaking in depth with our clients, what they most need is a mobile friendly web application.
Developing phone applications on the web for WebKit based mobile browsers using HTML5 means that our clients can by-pass the App Store submission, work on both Android and iPHone platforms (and many others) and even work offline in Airplane Mode!
WebKit based mobile browsers include: Safari Mobile, Google's Android Browser, Web Browser S60 (used on Nokia, Samsung and LG phones). The entire Operating System for the new Palm phones: WebOS, is based on WebKit as well.
Of course, WebKit supports many desktop browsers as well most notably Apple's Safari and Google's Chrome. FireFox, based on Mozilla, has been offering great support for HTML5 as well.