1. Introduction
HTML has been in continuous evolution since it was introduced to the Internet in the early 1990's. Some features were introduced in specifications; others were introduced in software releases. In some respects, implementations and author practices have converged with each other and with specifications and standards, but in other ways, they continue to diverge.
HTML 4 became a W3C Recommendation in 1997. While it continues to serve as a rough guide to many of the core features of HTML, it does not provide enough information to build implementations that interoperate with each other and, more importantly, with a critical mass of deployed content. The same goes for XHTML1, which defines an XML serialization for HTML 4, and DOM Level 2 HTML, which defines JavaScript APIs for both HTML and XHTML.
The HTML 5 draft reflects an effort, started in 2004, to study contemporary HTML implementations and deployed content. The draft:
* Defines a single language called HTML 5 which can be written in a "custom" HTML syntax and in XML syntax.
* Defines detailed processing models to foster interoperable implementations.
* Improves markup for documents.
* The following elements have been introduced for better structure:
* Introduces markup and APIs for emerging idioms, such as Web applications.
2. New Elements
* section represents a generic document or application section. It can be used together with h1-h6 to indicate the document structure.
* article represents an independent piece of content of a document, such as a blog entry or newspaper article.
* aside represents a piece of content that is only slightly related to the rest of the page.
* header represents the header of a section.
* footer represents a footer for a section and can contain information about the author, copyright information, et cetera.
* nav represents a section of the document intended for navigation.
* dialog can be used to mark up a conversation like this:
Costello
Look, you gotta first baseman?
Abbott
Certainly.
Costello
Who's playing first?
Abbott
That's right.
Costello
When you pay off the first baseman every month, who gets the money?
Abbott
Every dollar of it.
* figure can be used to associate a caption together with some embedded content, such as a graphic or video:
…
Example
Then there are several other new elements:
* audio and video for multimedia content. Both provide an API so application authors can script their own user interface, but there is also a way to trigger a user interface provided by the user agent. source elements are used together with these elements if there are multiple streams available of different types.
* embed is used for plugin content.
* mark represents a run of marked text.
* meter represents a measurement, such as disk usage.
* time represents a date and/or time.
* canvas is used for rendering dynamic bitmap graphics on the fly, such as graphs, games, et cetera.
* command represents a command the user can invoke.
* datagrid represents an interactive representation of a tree list or tabular data.
* details represents additional information or controls which the user can obtain on demand.
* datalist together with the a new list attribute for input is used to make comboboxes:
* datatemplate, rule and nest elements provide a templating mechanism for HTML.
* event-source is used to "catch" server sent events.
* output represents some type of output, such as from a calculation done through scripting.
* progress represents a completion of a task, such as downloading or when performing a series of expensive operations.
* The ruby, rt and rb elements allow for marking up ruby annotations.
The input element's type attribute now has the following new values:
* datetime
* datetime-local
* date
* month
* week
* time
* number
* range
* email
* url
The idea of these new types is that the user agent can provide the user interface, such as a calendar date picker or integration with the user's address book and submit a defined format to the server. It gives the user a better experience as his input is checked before sending it to the server meaning there is less time to wait for feedback.
3. New Attributes
HTML 5 has introduced several new attributes to various elements that were already part of HTML 4:
* The a and area elements now have a media attribute for consistency with the link element. It is purely advisory.
* The a and area elements have a new attribute called ping that specifies a space separated list of URIs which have to be pinged when the hyperlink is followed. Currently user tracking is mostly done through redirects. This attribute allows the user agent to inform users which URIs are going to be pinged as well as giving privacy-conscious users a way to turn it off.
* The area element, for consistency, now has the hreflang and rel attributes.
* The base element can now have a target attribute as well mainly for consistency with the atarget attribute for the a and area elements is no longer deprecated, as it is useful in Web applications, for example in conjunction with iframe.
* The value attribute for the li element is no longer deprecated as it is not presentational. The same goes for the start attribute of the ol element.
* The meta element has a charset attribute now as this was already supported and provides a nicer way to specify the character encoding for the document.
* A new autofocus attribute can be specified on the input (except when the type attribute is hidden), select, textarea and button elements. It provides a declarative way to focus a form control during page load. Using this feature should enhance the user experience as the user can turn it off if he does not like it, for instance.
* The new form attribute for input, output, select, textarea, button and fieldset elements allows for controls to be associated with more than a single form.
* The input, button and form elements have a new replace attribute which affects what will be done with the document after a form has been submitted.
* The form and select elements (as well as the datalist element) have a data attribute that allows for automatically prefilling of form controls, in case of form, or the form control, in case of select and datalist, with data from the server.
* The new required attribute applies to input (except when the type attribute is hidden, imagesubmit) and textarea. It indicates that the user has to fill in a value in order to submit the form. or some button type such as
* The input and textarea elements have a new attribute called inputmode which gives a hint to the user interface as to what kind of input is expected.
* You can now disable an entire fieldset by using the disabled attribute on it. This was not possible before.
* The input element has several new attributes to specify constraints: autocomplete, min, max, pattern and step. As mentioned before it also has a new list attribute which can be used together with the datalist and select element.
* input and button also have a new template attribute which can be used for repetition templates.
* The menu element has three new attributes: type, label and autosubmit. They allow the element to transform into a menu as found in typical user interfaces as well as providing for context menus in conjunction with the global contextmenu attribute.
* The style element has a new scoped attribute which can be used to enable scoped style sheets. Style rules within such a style element only apply to the local tree.
* The script element has a new attribute called async that influences script loading and execution.
* The html element has a new attribute called manifest that points to an application cache manifest used in conjunction with the API for offline Web applications.
* The link element has a new attribute called sizes. It can be used in conjunction with the iconrel attribute) to indicate the size of the referenced icon. relationship (set through the
* The ol element has a new attribute called reversed to indicate that the list order is descending when present.
* The iframe element has two new attributes called seamless and sandbox which allow for sandboxing content, e.g. blog comments.
Several attributes from HTML 4 now apply to all elements. These are called global attributes: class, dir, id, lang, style, tabindex and title.
There are also several new global attributes:
* The contenteditable attribute indicates that the element is an editable area. The user can change the contents of the element and manipulate the markup.
* The contextmenu attribute can be used to point to a context menu provided by the author.
* The draggable attribute can be used together with the new drag & drop API.
* The irrelevant attribute indicates that an element is not yet, or is no longer, relevant.
* The ref, registrationmark and template global attributes complement the data template feature.
* The data-* collection of author defined attributes. Authors can define any attribute they want as long as they prefix it with data- to avoid clashes with future versions of HTML. The only requirement on these attributes is that they are not used for user agent extensions.
The following are the attributes for the repetition model. These are global attributes and as such may be used on all HTML elements, or on any element in any other namespace, with the attributes being in the http://www.w3.org/1999/xhtml namespace.:
* repeat
* repeat-start
* repeat-min
* repeat-max
HTML 5 also makes all event handler attributes from HTML 4 that take the form onevent-nameonmessage attribute which can be used together with the new event-source element and the cross-document messaging API. global attributes and adds several new event handler attributes for new events it defines, such as the
4. Changed Elements
These elements have slightly modified meanings in HTML 5 to better reflect how they are used on the Web or to make them more useful:
* The a element without an href attribute now represents a "placeholder link".
* The address element is now scoped by the new concept of sectioning.
* The b element now represents a span of text to be stylistically offset from the normal prose without conveying any extra importance, such as key words in a document abstract, product names in a review, or other spans of text whose typical typographic presentation is emboldened.
* The hr element now represents a paragraph-level thematic break.
* The i element now represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized. Usage varies widely by language.
*
For the label element the browser should no longer move focus from the label to the control unless such behaviour is standard for the underlying platform user interface.
* The menu element is redefined to be useful for actual menus.
* The small element now represents small print (for side comments and legal print).
* The strong element now represents importance rather than strong emphasis.
* Quotation marks for the q element are now to be provided by the author rather than the user agent.
5. Absent Elements
The elements in this section are not to be used by authors. User agents will still have to support them and HTML 5 will get a rendering section in due course that says exactly how. (The isindex element for instance is already supported by the parser.)
The following elements are not in HTML 5 because their effect is purely presentational and therefore better handled by CSS:
* basefont
* big
* center
* font
* s
* strike
* tt
* u
The following elements are not in HTML 5 because their usage affected usability and accessibility for the end user in a negative way:
* frame
* frameset
* noframes
The following elements are not included because they have not been used often, created confusion or can be handled by other elements:
* acronym is not included because it has created lots of confusion. Authors are to use abbr for abbreviations.
* applet has been obsoleted in favor of object.
* isindex usage can be replaced by usage of form controls.
* dir has been obsoleted in favor of ul.
Finally the noscript is only conforming in the HTML syntax. It is not included in the XML syntax as its usage relies on an HTML parser.
6. Absent Attributes
Some attributes from HTML 4 are no longer allowed in HTML 5. If they need to have any impact on user agents for compatibility reasons it is defined how they should work in those scenarios.
* accesskey attribute on a, area, button, input, label, legend and textarea.
* rev and charset attributes on link and a.
* shape and coords attributes on a.
* longdesc attribute on img and iframe.
* target attribute on link.
* nohref attribute on area.
* profile attribute on head.
* version attribute on html.
* name attribute on img, form and a (use id instead).
* scheme attribute on meta.
* archive, classid, codebase, codetype, declare and standby attributes on object.
* valuetype and type attributes on param.
* language attribute on script.
* summary attribute on table.
* axis and abbr attributes on td and th.
* scope attribute on td.
* headers attribute on th.
In addition, HTML 5 has none of the presentational attributes that were in HTML 4 as they are better handled by CSS:
* align attribute on caption, iframe, img, input, object, legend, table, hr, div, h1, h2, h3, h4, h5, h6, p, col, colgroup, tbody, td, tfoot, th, thead and tr.
* alink, link, text and vlink attributes on body.
* background attribute on body.
* bgcolor attribute on table, tr, td, th and body.
* border attribute on table, img and object.
* cellpadding and cellspacing attributes on table.
* char and charoff attributes on col, colgroup, tbody, td, tfoot, th, thead and tr.
* clear attribute on br.
* compact attribute on dl, menu, ol and ul.
* frame attribute on table.
* frameborder attribute on iframe.
* height attribute on td and th.
* hspace and vspace attributes on img and object.
* marginheight and marginwidth attributes on iframe.
* noshade attribute on hr.
* nowrap attribute on td and th.
* rules attribute on table.
* scrolling attribute on iframe.
* size attribute on hr, input and select.
* type attribute on li, ol and ul.
* valign attribute on col, colgroup, tbody, td, tfoot, th, thead and tr.
* width attribute on hr, table, td, th, col, colgroup and pre.
7. APIs
HTML 5 introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications:
* 2D drawing API which can be used with the new canvas element.
* API for playing of video and audio which can be used with the new video and audio elements.
* Persistent storage. Both key / value and a SQL database are supported.
* An API that enables offline Web applications.
* An API that allows a Web application to register itself for certain protocols or MIME types.
* Editing API in combination with a new global contenteditable attribute.
* Drag & drop API in combination with a draggable attribute.
* Network API.
* API that exposes the history and allows pages to add to it to prevent breaking the back button. (This API has the necessary security restrictions in place.)
* Cross-document messaging.
* Server-sent events in combination with the new event-source element.
* Notification API to alert the user to new information, such as new e-mail messages in an e-mail application.
7.1 Extensions to HTMLDocument
HTML 5 has extended the HTMLDocument interface from DOM Level 2 HTML in a number of ways. The interface is now implemented on all objects implementing the Document interface so it stays meaningful in a compound document context. It also has several noteworthy new members:
* getElementsByClassName() to select elements by their class name. The way this method is defined it will allow it to work for any content with class attributes and a Document object such as SVG and MathML.
* innerHTML as an easy way to parse and serialize an HTML or XML document. This attribute was previously only available on HTMLElement in Web browsers and not part of any standard.
* activeElement and hasFocus to determine which element is currently focused and whether the Document has focus respectively.
* getSelection() which returns an object that represents the current selection(s).
* designMode and execCommand() which are mostly used for editing of documents.
7.2 Extensions to HTMLElement
The HTMLElement interface has also gained several extensions in HTML 5:
* getElementsByClassName() which is basically a scoped version of the one found on HTMLDocument.
* innerHTML as found in Web browsers today. It is also defined to work in XML context (when it is used in an XML document).
* classList is a convenient accessor for className. The object it returns exposes methods, such as has(), add(), remove() and toggle() for manipulating the element's classes. The a, area and link elements have a similar attribute called relList that provides the same functionality for the rel attribute
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