Post in HTML 5

HTML is the core language of the World Wide Web. The W3C publishes HTML5, which is the fifth major revision of HTML. The WHATWG publishes HTML, which is a rough superset of HTML5. "HTML5 differences from HTML4" describes the differences of these documents from HTML4, and calls out cases where HTML is different from HTML5. This document may not provide accurate information as the specifications are still actively in development. When in doubt, always check the specifications themselves

• Support for mutation observers was added.
• The TextTrackCue members alignment, linePosition, textPosition and direction were renamed to align, line, position and vertical, respectively.
• The command element now has a command attribute.
• Drag and drop content is now suggested to be filtered by user agents to prevent XSS attacks.
• The translate global attribute was added.
• The showModalDialog(), alert(), confirm() and prompt() methods are now allowed to do nothing during pagehide, beforeunload and unload events.
• The script element now supports beforescriptexecute and afterscriptexecute events.
• window.onerror now supports a fourth argument for column position.
• The window.opener IDL attribute can now return null in some cases.
• The clearTimeout() and clearInterval() methods were made synonymous.
• The CSS @global at-rule was introduced, for use together with style elements with the scoped attribute.
• The embed and object elements now have a legacy caller.
• The handling of window.onerror's return value was changed to match reality.
• The setTimeout() API is now allowed to be throttled in background tabs.
• The :valid and :invalid pseudo-classes now apply to form elements.
• The toBlob() method on canvas now honors the origin-clean flag.
• The activeElement IDL attribute now points to the relevant browsing context container (e.g. iframe) when a child document has focus.
• The atob() method now ignores whitespace.
• The dropzone attribute was changed to use "string:" and "file:" instead of "s:" and "f:".
• The HTML parser was fixed to correctly handle a case involving foreign lands and foster parenting.
• The date-and-time microsyntaxes now allows a single space instead of a "T".
• Application cache no longer checks the MIME type of the cache manifest.
• The cueAsSource IDL attribute on TextTrackCue got renamed to text.
• The window.onerror API is now invoked with dummy arguments for cross-origin scripts.
• The textarea element's value and textLength IDL attributes have their newlines normalized to LF.
• The q element now has language-specific quotes rendered by default.
• The data element was introduced.
• The time element was redesigned to make it match how people wanted to use it. Its pubdate attribute was dropped.
• The legacy caller on form was removed.
• The location.resolveURL() method was removed.
• The track element now sniffs instead of obeying the MIME type.
• The load() method on documents created by createDocument() is now defined on the XMLDocument interface.
• Members of HTMLDocument moved to Document and window.HTMLDocument now just returns window.Document.
• The MutableTextTrack and TextTrack interfaces were merged and TextTrackCue was made more mutable.
• The selectedOption IDL attribute on input was dropped.
• Attribute values in Selectors are now case sensitive for all attributes.
• The readyState IDL attribute moved from TextTrack to HTMLTrackElement.
• The text/html-sandboxed MIME type was dropped.
• Floating point numbers are now allowed to begin with a "." character.
• Navigating to an audio or video resource is now supported.
• Table cells now allow flow content but does not allow header, footer, sectioning content or heading content descendants.
• Adding a track to a media element now fires an addtrack event on the relevant track list objects.
• Setting currentTime on media elements before the media has loaded now defers the seek instead of throwing.
• Plugins are no longer disabled in sandboxed iframes if they honor the sandbox attribute.
• Some tweaks to history navigation and related events.
• Media elements and MediaControllers now get paused when they end.
• Events now support constructors and some init*Event() methods were removed.
• Media elements now fire a suspend event when the resource is loaded.
• Form submission now normalizes newlines to CRLF.
• Some tweaks around bidi and the br element.
• Large parts of the Editing section moved to HTML Editing APIs.
• UndoManager and related features moved to UndoManager and DOM Transaction.
• isProtocolHandlerRegistered(), isContentHandlerRegistered(), unregisterProtocolHandler() and unregisterContentHandler() were added.
• registerContentHandler() now has a blacklist of MIME types.
• registerProtocolHandler() now has a whitelist of protocols, but also supports any protocol that starts with "web+".
• Fragment identifiers for text/html resources now don't need to point to an element with a matching ID.
• audio elements are now allowed to have zero source children.
• There are now some restrictions on the use of bidi formatting characters.
• The maxlength and size attributes are allowed (but give warnings in validators) on input elements with type=number.
• The link relation "shortcut icon" is now allowed.
• Heading elements are now allowed to have the heading and tab roles.
• Things that use EventTarget now inherit from it instead of using "implements".
• The setInterval() API now clamps to 4ms instead of 10ms.
• The select element and its options collection now have a setter.
• rel=help on links now show a help cursor by default.
• Calls to window.print() before the document is loaded defers the print until it is loaded.
• Application cache gained an abort() method.
• HTMLCollection, DOMTokenList, getElementsByClassName(), createHTMLDocument(), HTML-specific overrides to some DOM Core features (like createElement()), some definitions, the id IDL attribute and ID handling moved to DOM4.
• Fragment identifiers can now survive redirects.
• The pushState() and replaceState() methods now change the history entry to GET.
• The command API now has its properties prefixed so they are now commandLabel, commandIcon, commandHidden, commandDisabled and commandChecked.
• The structured clone algorithm now supports sparse arrays.
• window.postMessage now supports transferring some objects instead of cloning them, and supports transferring ArrayBuffer.
• Application cache was made stricter in its MIME type checking.
• The placeholder attribute is now allowed on input elements with type=number.
• MediaController gained an onended event listener.
• The HTML parser changed its handling of U+0000 characters in some places.
• The object element gained a new attribute typemustmatch, to make it safer for authors to embed untrusted resources where they expect a certain content type.
• The form attribute was removed from meter and progress.
• The HTML parser was made more forward compatible in its handling of ruby.
• Some MIME types (e.g. text/plain) that are guaranteed to never be supported as scripting types for script were specified, so authors can safely use them for custom data blocks.
• about:blank documents created from window.open() now get a load event.
• window.status was specified to exist but do nothing.
• Drag and drop DataTransferItems was renamed to DataTransferItemList.
• Application cache now supports 'no-store' and HTTPS.
• The structured clone algorithm now supports getters.
• The crossorigin attribute has been added to img, video and audio to use CORS.
• The external IDL attribute has been added on window and has the members AddSearchProvider() and IsSearchProviderInstalled().

Further changes to WHATWG HTML that do not affect HTML5:

• The 2d context now supports ellipses with the arc() and arcTo() methods and the new ellipse() method.
• The 2d context now supports Path objects. SVG path data can be added to a Path.
• The http+aes: and https+aes: URL schemes were added to allow sensitive resources to be held on untrusted servers.
• When the itemprop attribute is used on an element where microdata gets its value from an attribute (like href on a elements), that attribute is now required.
• PeerConnection was moved to WebRTC.
• WebVTT was moved to its own specification.
• WebSockets no longer receive messages in the CLOSING state.
• The Atom conversion algorithm was dropped.
• The itemtype attribute now allows multiple types.
• CanvasPixelArray was dropped in favor of Uint8ClampedArray.
• The microdata to RDF conversion algorithm was dropped.
• The link element is no longer allowed to have both rel and itemprop.
• WebSocket API disallows opening an insecure connection if the document uses a secure connection.
• The "storage mutex" is made optional.
• Web Storage no longer supports structured data.
• The a element got a new download attribute. This attribute is not included in HTML5.
• An experimental specification for the window.find() method was added.
• The 2d context fillText() and strokeText() methods now do not collapse whitespace.
• Microdata now handles infinite loops.
• Web Worker location now stringifies.
• Script errors in a Web Worker can now be detected in a parent worker or the document with the onerror handler.
• EventSource now supports CORS.
• EventSource was made stricter in its MIME type checking.
• Web Workers gained the atob() and btoa() methods.
• Web Workers gained the ononline and onoffline event handlers.
• WebSockets API has the error event again.
• WebSockets API now exposes the selected extensions.
• Various tweaks to the UDP PeerConnection API.
• WebSocket close code and reason are now supported in the API.
• Binary data is now supported in WebSockets.
• Redirects in WebSockets are now blocked for security reasons.

6.2 Changes from 5 April 2011 to 25 May 2011

• Support for the javascript: scheme in img, object, CSS, etc, has been dropped.
• The toBlob() method has been added to canvas.
• The drawFocusRing() method on the canvas 2d context has been split into two methods, drawSystemFocusRing() and drawCustomFocusRing().
• The values attribute on PropertyNodeList has been replaced with a getValues() method.
• The select event has been specified.
• The selectDirection IDL attribute has been added to input and textarea.
• The :enabled and :disabled pseudo-classes now match fieldset, and the :indeterminate pseudo-class can now match progress.
• The getKind() method has been added to TrackList.
• The MediaController API and the mediagroup attribute have been added to synchronize playback of media elements.
• Some ARIA defaults have changed, and it is now invalid to specify ARIA attributes that match the defaults.
• The getName() method on TrackList was renamed to getLabel().
• The border attribute on table is now conforming.
• The u element is now conforming.
• The summary attribute on table is now non-conforming.
• The audio attribute on video was changed to a boolean muted attribute.
• The Content-Language meta pragma is now non-conforming.

6.3 Changes from 13 January 2011 to 5 April 2011

• The pushState and replaceState features have been changed based on implementation feedback in Firefox, and history.state has been introduced.
• The tracks IDL attribute on media elements has been renamed to textTracks.
• Event handler content attributes now support ECMAScript strict mode.
• The forminput and formchange events, and the dispatchFormInput() and dispatchFormChange() methods have been dropped.
• The rel keywords archives, up, last, index, first and related synonyms have been dropped.
• Removing a media element from the DOM and inserting it again in the same script now doesn't pause the media element.
• The video element's letterboxing rules are now specified in terms of CSS 'object-fit'.
• Cross-origin fonts now don't leak information about the font when drawn on a canvas.
• The character encoding declaration is now allowed to be within the first 1024 bytes instead of the first 512 bytes.
• The onerror event handler on window is now invoked for compile-time script errors as well as runtime errors.
• Script-inserted script elements now have async default to true, which can be set to false to make the scripts execute in insertion order.
• The atob() and btoa() methods have been specified.
• The suggested file extension for application cache manifest files has been changed from .manifest to .appcache.
• The action and formaction attributes are no longer allowed to have the empty string as value.

6.4 Changes from 19 October 2010 to 13 January 2011

• Drag and drop model was refined.
• A new global dropzone attribute was added.
• A new bdi element was added to aid with user-generated content that may have bidi implications.
• The dir attribute gained a new "auto" value.
• A dirname attribute was added to input elements. When specified the directionality as specified by the user will be submitted to the server as well.
• A new track element and associated TextTrack API were added for video text tracks.
• The type attribute on the ol element is now allowed.

The getSelection() API moved to a separate DOM Range draft. Similarly UndoManager has been removed from the W3C copy of HTML5 for now as it is not ready yet.

6.5 Changes from 24 June 2010 to 19 October 2010

• Numerous changes to the HTML parsing algorithm based on implementation feedback.
• The hidden attribute now works for table-related elements.
• The canvas getContext() method is now defined to be able to handle multiple contexts better.
• The media elements' startTime IDL attribute was renamed to initialTime and startOffsetTime was added.
• The prefetch link relationship can now be used on a elements.
• The datetime attribute of ins and del no longer requires a time to be specified.
• Using PUT and DELETE as HTTP methods for the form element is no longer supported.
• The s element is no longer deprecated.
• The video element has a new audio attribute.

Per usual, lots of other minor fixes have been made as well.

6.6 Changes from 4 March 2010 to 24 June 2010

• The ping attribute has been removed from the W3C version of HTML5.
• The title element is optional for iframe srcdoc documents and other scenarios where a title is already available. As is the case with email.
• keywords is now a standard metadata name for the meta element.
• The allow-top-navigation value has been added for the sandbox attribute on the iframe element. It allows the embedded content to navigate its parent when specified.
• The wbr element has been added.
• The alternate keyword for the rel attribute of the link element can now be used to point to feeds again, even if the feed is not an alternative for the document.
• The HTML to Atom mapping has been removed from the W3C version of HTML5.

In addition lots of minor changes, clarifications, and fixes have been made to the document.

6.7 Changes from 25 August 2009 to 4 March 2010

• The dialog element has been removed. A section with advice on how to mark up conversations has effectively replaced it.
• document.head has been introduced to provide convenient access to the head element from script.
• The link type feed has been removed. alternate with specific media types is to be used instead.
• createHTMLDocument() has been introduced as API to allow easy creation of HTML documents.
• Both the meter and progress elements no longer have "magic" processing of their contents because it could not be made to work internationally.
• The meter and progress elements, as well as the output element, can now be labeled using the label element.
• A new media type, text/html-sandboxed, was introduced to allow hosting of potentially hostile content without it causing harm.
• A srcdoc attribute for the iframe element was introduced to allow embedding of potentially hostile content inline. It is expected to be used together with the sandbox and seamless attributes.
• The figure element now uses a new element figcaption rather than legend because people want to use HTML5 long before it reaches W3C Recommendation.
• The details element now uses a new element summary for exactly the same reason.
• The autobuffer attribute on media elements was renamed to preload.

A whole lot of other smaller issues have also been resolved. The above list summarizes what is thought to be of primary interest to authors.
In addition to all of the above, Microdata, the 2D context API for canvas, and Web Messaging (postMessage() API) have been split into their own drafts at the W3C (the WHATWG still publishes a version of HTML5 that includes them):

• HTML Microdata
• HTML Canvas 2D Context
• HTML5 Web Messaging

Specific microdata vocabularies are gone altogether in the W3C draft of HTML5 and are not published as a separate draft. The WHATWG draft of HTML5 still includes them.

6.8 Changes from 23 April 2009 to 25 August 2009

• When the time element is empty user agents have to render the time in a locale-specific manner.
• The load event is dispatched at Window, but now has Document as its target.
• pushState() now affects the Referer (sic) header.
• onundo and onredo are now on Window.
• Media elements now have a startTime member that indicates where the current resource starts.
• header has been renamed to hgroup and a new header element has been introduced.
• createImageData() now also takes ImageData objects.
• createPattern() can now take a video element as argument too.
• The footer element is no longer allowed in header and header is not allowed in address or footer.
• A new control has been introduced: <input type="tel">
• The Command API now works for all elements.
• accesskey is now properly defined.
• section and article now take a cite attribute.
• A new feature called Microdata has been introduced which allows people to embed custom data structures in their HTML documents.
• Using the Microdata model three predefined vocabularies have also been included: vCard, vEvent, and a model for licensing.
• Drag and drop has been updated to work with the Microdata model.
• The last of the parsing quirks has been defined.
• textLength has been added as member of the textarea element.
• The rp element now takes phrasing content rather than a single character.
• location.reload() is now defined.
• The hashchange event now fires asynchronously.
• Rules for compatibility with XPath 1.0 and XSLT 1.0 have been added.
• The spellcheck IDL attribute now maps to a DOMString.
• hasFeature() support has been reduced to a minimum.
• The Audio() constructor sets the autobuffer attribute.
• The td element is no longer allowed in thead.
• The input element and DataTransfer object now have a files IDL attribute.
• The datagrid and bb have been removed due to their design not being agreed upon.
• The cue range API has been removed from the media elements.
• Support for WAI-ARIA has been integrated.

On top of this list quite a few minor clarifications, typos, issues specific to implementors, and other small problems have been resolved.
In addition, the following parts of HTML5 have been taken out and will likely be further developed at the IETF:

• Definition of URLs.
• Definition of Content-Type sniffing.

6.9 Changes from 12 February 2009 to 23 April 2009

• A new global attribute called spellcheck has been added.
• Defined that ECMAScript this in the global object returns a WindowProxy object rather than the Window object.
• The value IDL attribute for input elements in the File Upload state is now defined.
• Definition of designMode was changed to be more in line with legacy implementations.
• The drawImage() method of the 2D drawing API can now take a video element as well.
• The way media elements load resources has been changed.
• document.domain is now IPv6-compatible.
• The video element gained an autobuffer boolean attribute that serves as a hint.
• You are now allowed to specify the meta element with a charset attribute in XML documents if the value of that attribute matches the encoding of the document. (Note that it does not specify the value, it is just a talisman.)
• The bufferingRate and bufferingThrottled members of media elements have been removed.
• The media element resource selection algorithm is now asynchronous.
• The postMessage() API now takes an array of MessagePort objects rather than just one.
• The second argument of the add() method on the select element and the options member of the select element is now optional.
• The action, enctype, method, novalidate, and target attributes on input and button elements have been renamed to formaction, formenctype, formmethod, formnovalidate, and formtarget.
• A "storage mutex" concept has been added to deal with separate pages trying to change a storage object (document.cookie and localStorage) at the same time. The Navigator gained a getStorageUpdates() method to allow it to be explicitly released.
• A syntax for SVG similar to MathML is now defined so that SVG can be included in text/html resources.
• The placeholder attribute has been added to the textarea element.
• Added a keygen element for key pair generation.
• The datagrid element was revised to make the API more asynchronous and allow for unloaded parts of the grid.

In addition, several parts of HTML5 have been taken out and will be further developed by the Web Applications Working Group as standalone specifications:

• WebSocket API
• WebSocket protocol
• Server-Sent Events
• Web Storage (localStorage and sessionStorage)
• Web SQL Database

6.10 Changes from 10 June 2008 to 12 February 2009

• The data member of ImageData objects has been changed from an array to a CanvasPixelArray object.
• Shadows are now required from implementations of the canvas element and its API.
• Security model for canvas is clarified.
• Various changes to the processing model of canvas have been made in response to implementation and author feedback. E.g. clarifying what happens when NaN and Infinity are passed and fixing the definitions of arc() and arcTo().
• innerHTML in XML was slightly changed to improve round-tripping.
• The toDataURL() method on the canvas element now supports setting a quality level when the media type argument is image/jpeg.
• The poster attribute of the video element now affects its intrinsic dimensions.
• The behavior of the type attribute of the link element has been clarified.
• Sniffing is now allowed for link when the expected type is an image.
• A section on URLs is introduced dealing with how URL values are to be interpreted and what exactly authors are required to do. Every feature of the specification that uses URLs has been reworded to take the new URL section into account.
• It is now explicit that the href attribute of the base element does not depend on xml:base.
• It is now defined what the behavior should be when the base URL changes.
• URL decomposition IDL attributes are now more aligned with Internet Explorer.
• The xmlns attribute with the value http://www.w3.org/1999/xhtml is now allowed on all HTML elements.
• data-* attributes and custom attributes on the embed element now have to match the XML Name production and cannot contain a colon.
• WebSocket API is introduced for bidirectional communication with a server.
• The default value of volume on media elements is now 1.0 rather than 0.5.
• event-source was renamed to eventsource because no other HTML element uses a hyphen.
• A message channel API has been introduced augmenting postMessage().
• A new element named bb has been added. It represents a user agent command that the user can invoke.
• The addCueRange() method on media elements has been modified to take an identifier which is exposed in the callbacks.
• It is now defined how to mutate a DOM into an infoset.
• The parent attribute of the Window object is now defined.
• The embed element is defined to do extension sniffing for compatibility with servers that deliver Flash as text/plain. (This is marked as an issue in the specification to figure out if there is a better way to make this work.)
• The embed can now be used without its src attribute.
• getElementsByClassName() is defined to be ASCII case-insensitive in quirks mode for consistency with CSS.
• In HTML documents localName no longer returns the node name in uppercase.
• data-* attributes are defined to be always lowercase.
• The opener attribute of the Window object is not to be present when the page was opened from a link with target="_blank" and rel="noreferrer".
• The top attribute of the Window object is now defined.
• The a element now allows nested flow content, but not nested interactive content.
• It is now defined what the header element means to document summaries and table of contents.
• What it means to fetch a resource is now defined.
• Patterns are now required for the canvas element.
• The autosubmit attribute has been removed from the menu element.
• Support for outerHTML and insertAdjacentHTML() has been added.
• xml:lang is now allowed in HTML when lang is also specified and they have the same value. In XML lang is allowed if xml:lang is also specified and they have the same value.
• The frameElement attribute of the Window object is now defined.
• An event loop and task queue is now defined detailing script execution and events. All features have been updated to be defined in terms of this mechanism.
• If the alt attribute is omitted a title attribute, an enclosing figure element with a legend element descendant, or an enclosing section with an associated heading must be present.
• The irrelevant attribute has been renamed to hidden.
• The definitionURL attribute of MathML is now properly supported. Previously it would have ended up being all lowercase during parsing.
• User agents must treat US-ASCII as Windows-1252 for compatibility reasons.
• An alternative syntax for the DOCTYPE is allowed for compatibility with some XML tools.
• Data templates have been removed (consisted of the datatemplate, rule and nest elements).
• The media elements now support just a single loop attribute.
• The load() method on media elements has been redefined as asynchronous. It also tries out files in turn now rather than just looking at the type attribute of the source element.
• A new member called canPlayType() has been added to the media elements.
• The totalBytes and bufferedBytes attributes have been removed from the media elements.
• The Location object gained a resolveURL() method.
• The q element has changed again. Punctuation is to be provided by the user agent again.
• Various changes were made to the HTML parser algorithm to be more in line with the behavior Web sites require.
• The unload and beforeunload events are now defined.
• The IDL blocks in the specification have been revamped to be in line with the upcoming Web IDL specification.
• Table headers can now have headers. User agents are required to support a headers attribute pointing to a td or th element, but authors are required to only let them point to th elements.
• Interested parties can now register new http-equiv values.
• When the meta element has a charset attribute it must occur within the first 512 bytes.
• The StorageEvent object now has a storageArea attribute.
• It is now defined how HTML is to be used within the SVG foreignObject element.
• The notification API has been dropped.
• How [[Get]] works for the HTMLDocument and Window objects is now defined.
• The Window object gained the locationbar, menubar, personalbar, scrollbars, statusbar and toolbar attributes giving information about the user interface.
• The application cache section has been significantly revised and updated.
• document.domain now relies on the Public Suffix List. [PSL]
• A non-normative rendering section has been added that describes user agent rendering rules for both obsolete and conforming elements.
• A normative section has been added that defines when certain selectors as defined in the Selectors and the CSS3 Basic User Interface Module match HTML elements. [SELECTORS] [CSSUI]

Web Forms 2.0, previously a standalone specification, has been fully integrated into HTML5 since last publication. The following changes were made to the forms chapter:

• Support for XML submission has been removed.
• Support for form filling has been removed.
• Support for filling of the select and datalist elements through the data attribute has been removed.
• Support for associating a field with multiple forms has been removed. A field can still be associated with a form it is not nested in through the form attribute.
• The dispatchChangeInput() and dispatchFormChange() methods have been removed from the select, input, textarea, and button elements.
• Repetition templates have been removed.
• The inputmode attribute has been removed.
• The input element in the File Upload state no longer supports the min and max attributes.
• The allow attribute on input elements in the File Upload state is no longer authoritative.
• The pattern and accept attributes for textarea have been removed.
• RFC 3106 is no longer explicitly supported.
• The submit() method now just submits, it no longer ensures the form controls are valid.
• The input element in the Range state now defaults to the middle, rather than the minimum value.
• The size attribute on the input element is now conforming (rather than deprecated).
• object elements now partake in form submission.
• The type attribute of the input element gained the values color and search.
• The input element gained a multiple attribute which allows for either multiple e-mails or multiple files to be uploaded depending on the value of the type attribute.
• The input, button and form elements now have a novalidate attribute to indicate that the form fields should not be required to have valid values upon submission.
• When the label element contains an input it may still have a for attribute as long as it points to the input element it contains.
• The input element now has an indeterminate IDL attribute.
• The input element gained a placeholder attribute.

6.11 Changes from 22 January 2008 to 10 June 2008

• Implementation and authoring details around the ping attribute have changed.
• <meta http-equiv=content-type> is now a conforming way to set the character encoding.
• API for the canvas element has been cleaned up. Text support has been added.
• globalStorage is now restricted to the same-origin policy and renamed to localStorage. Related event dispatching has been clarified.
• postMessage() API changed. Only the origin of the message is exposed, no longer the URL. It also requires a second argument that indicates the origin of the target document.
• Drag and drop API has got clarification. The dataTransfer object now has a types attribute indicating the type of data being transferred.
• The m element is now called mark.
• Server-sent events has changed and gotten clarification. It uses a new format so that older implementations are not broken.
• The figure element no longer requires a caption.
• The ol element has a new reversed attribute.
• Character encoding detection has changed in response to feedback.
• Various changes have been made to the HTML parser section in response to implementation feedback.
• Various changes to the editing section have been made, including adding queryCommandEnabled() and related methods.
• The headers attribute has been added for td elements.
• The table element has a new createTBody() method.
• MathML support has been added to the HTML parser section. (SVG support is still awaiting input from the SVG WG.)
• Author-defined attributes have been added. Authors can add attributes to elements in the form of data-name and can access these through the DOM using dataset[name] on the element in question.
• The q element has changed to require punctuation inside rather than having the browser render it.
• The target attribute can now have the value _blank.
• The showModalDialog API has been added.
• The document.domain API has been defined.
• The source element now has a new pixelratio attribute useful for videos that have some kind encoding error.
• bufferedBytes, totalBytes and bufferingThrottled IDL attributes have been added to the video element.
• Media begin event has been renamed to loadstart for consistency with the Progress Events specification.
• charset attribute has been added to script.
• The iframe element has gained the sandbox and seamless attributes which provide sandboxing functionality.
• The ruby, rt and rp elements have been added to support ruby annotation.
• A showNotification() method has been added to show notification messages to the user.
• Support for beforeprint and afterprint events has been added.

Acknowledgments

The editors would like to thank Ben Millard, Bruce Lawson, Cameron McCormack, Charles McCathieNevile, Dan Connolly, David Håsäther, Dennis German, Frank Ellermann, Frank Palinkas, Futomi Hatano, Gordon P. Hemsley, Henri Sivonen, James Graham, Jens Meiert, Jeremy Keith, Jürgen Jeka, Krijn Hoetmer, Leif Halvard Silli, Maciej Stachowiak, Mallory van Achterberg, Marcos Caceres, Mark Pilgrim, Martijn Wargers, Martyn Haigh, Masataka Yakura, Michael Smith, Mike Taylor, Ms2ger, Olivier Gendrin, Øistein E. Andersen, Philip Jägenstedt, Philip Taylor, Randy Peterman, Toby Inkster, and Yngve Spjeld Landro for their contributions to this document as well as to all the people who have contributed to HTML over the years for improving the Web!
Courtesy:http://www.w3.org/TR/2012/WD-html5-diff-20120329/#changelog