The Arrival of HTML 5: Lots of New Features

"HTML (Hyper Text Markup Language) is one of the underpinnings
technologies of the modern web with the lion's share of web users'
Internet activities founded on it. HTML now stands on the brink of
the next change -- the coming of HTML 5. At present, the Internet
already contains a handful of HTML 5 specification outlines which
partially cover HTML 5 features and conceptions. In this article, we
review the current state of HTML and describe the most significant
HTML 5 innovations.

Offline Potential: Some time ago, a new specification for client-side
database support with interesting applications was introduced. While
this feature had vast potential, it has been excluded from current
specification drafts due to insufficient interest from vendors which
use various SQL back-ends. As such, the only offline feature currently
available in HTML 5 is flexible online/offline resources management
using cache manifests. Cache manifests allow an author of a document
to specify which referenced resources must be cached in browser data
store (e.g., static images, external CSS and JavaScript files) and
which must be retrieved from a server (e.g., time-sensitive data like
stock price graphs, responses from web services invoked from within
JavaScript). The manifest also provides means for specifying fallback
offline replacements for resources which must not be cached. This
mechanism gives the ability to compose HTML documents which can be
viewed offline.

REST in Forms: REST application can be characterized by a clear
separation between clients and servers, stateless communications with
the server (no client context is stored on the server between requests)
and uniform client-server protocol that can be easily invoked from other
clients. Applied to HTTP, it encourages usage of URI for identifying
all entities and standard HTTP methods like GET (retrieve), POST (change),
PUT (add) and DELETE (remove) for entity operations. HTML 5 now fully
supports issuing PUT and DELETE requests from HTML forms without any
workarounds. This is an unobtrusive, but ideologically important
innovation which brings more elegance into web architecture and simplifies
development of HTML UI for REST services.

Communicating Documents: Now documents opened in browsers can exchange
data using messages. Such data exchange may be useful on a web page
that includes several frames with the data loaded from different origins.
Usually, a browser does not allow JavaScript code to access/manipulate
the objects of other documents opened from a different origin. This is
done to prevent cross-site scripting and other malicious and destructive
endeavors..." More Info See also HTML5 differences from HTML4:

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Courtesy:http://realworldxml.blogspot.com/2010/08/arrival-of-html-5-lots-of-new-features.html