A Platform for Web Development

A lot of the new features of HTML center around creating a better
platform for web-based applications. From more descriptive tags and
better cross-site and cross-window communication to animations and
improved multimedia support, developers using HTML5 have a lot of
new tools to build better user experiences.
More Descriptive Markup
Each version of HTML introduces some new markup, but never before
have there been so many new additions that directly relate to describing
content. You’ll learn about elements for defining headings, footers,
navigation sections, sidebars, and articles in Chapter 2, New Structural
Tags and Attributes, on page 24. You’ll also learn about meters,
progress bars, and how custom data attributes can help you mark up
data.

Multimedia with Less Reliance on Plug-ins
You don’t need Flash or Silverlight for video, audio, and vector graphics
anymore. Although Flash-based video players are relatively simple
to use, they don’t work on Apple’s mobile devices. That’s a significant
market, so you’ll need to learn how to use non-Flash video alternatives.
In Chapter 7, Embedding Audio and Video, on page 127, you’ll see how
to use HTML5 audio and video with effective fallbacks.
Better Applications
Developers have tried all kinds of things to make richer, more interactive
applications on the We b, from ActiveX controls to Flash. HTML5
offers amazing features that, in some cases, completely eliminate the
need for third-party technologies.
Cross-Document Messaging
We b browsers prevent us from using scripts on one domain to affect
or interact with scripts on another domain. This restriction keeps end
users safe from cross-site scripting, which has been used to do all sorts
of nasty things to unsuspecting site visitors.
However, this prevents all scripts from working, even when we write
them ourselves and know we can trust the content. HTML5 includes a
workaround that is both safe and simple to implement. You’ll see how
to make this work in Talking Across Domains,

Web Sockets
HTML5 offers support for We b Sockets, which give you a persistent
connection to a server. Instead of constantly polling a back end for
progress updates, your web page can subscribe to a socket, and the
back end can push notifications to your users. We’ll play with that a bit
in Chatting with Web Sockets