The purpose and application of HTML has grown considerably since its initial invention in 1994. HTML5 along with CSS3 address many of the major growing pains that HTML has encountered as it's been extended to be used as the foundation for web applications, mobile applications, ebooks, and a variety of other uses. HTML5 has the particular benefit of having reasonably wide support on mobile, and thus provides a comparatively stable up-level foundation for mobile web sites and applications; this is particularly valuable due to a variety of technologies it is often associated with that have particular benefits on mobile, such as location services and offline storage. Additionally, HTML5 and its related technologies help unify the capabilities of sophisticated web-based applications by allowing use of vector graphics (via canvas), standards-based videos (via video), and an extensible data model (via the data attribute).

As with any new standard, the support for HTML5 varies by browser. No single browser has universal support for HTML5, and some vary in their interpretations of the specification (albeit not to the same degree as previous standards). As a result, while HTML5 may provide a promising option for web applications with a reliable client profile, many websites will need to continue to provide down-level compatibility to account for browser differences and distribution. While HTML5 is a large step forward, this prevents it from being a universal foundation for all web projects.

HTML5 is the preferred presentation layer for websites, web applications and even mobile applications which are targeting a consistent device and browser profile which supports HTML5. For instance, it is Ignia's preferred technique for building many types of mobile applications, via PhoneGap or Chakra. HTML5 is also ideal for up-level features which are not required to be supported on down-level clients; for instance, while server-side form validation may be required for all devices, it may be acceptable for client-side form validation and masking to only be supported on modern browsers. As with all client-side technologies, the decision on when to apply HTML5 and related technologies needs to be driven by the client requirements, which in turns should be based on an analysis of the distribution of device capabilities associated with the target market(s) and demographic(s).

Ignia has a well-established set of best practices for HTML, including naming conventions, formatting standards, and usage guidelines.  The vast majority of these continue to remain relevant for HTML5.  In addition, in order to take advantage of HTML5 capabilities while maintaining down-level support browsers that either don't support HTML5, or which may not be fully compliant, Ignia recommends the use of Modernizr.