Markup
HTML5 introduces elements and attributes that reflect typical usage on modern websites. Some of them are semantic replacements for common uses of generic block (
<div>) and inline (<span>) elements, for example <nav> (website navigation block), <footer> (usually referring to bottom of web page or to last lines of HTML code), or <audio> and<video> instead of <object>.Some deprecated elements from HTML 4.01 have been dropped, including purely presentational elements such as <font> and<center>, whose effects have long been superseded by the more capable Cascading Style Sheets. There is also a renewed emphasis on the importance of DOM scripting(e.g., JavaScript) in Web behavior.
The HTML5 syntax is no longer based on SGMLdespite the similarity of its markup. It has, however, been designed to be backward compatible with common parsing of older versions of HTML. It comes with a new introductory line that looks like an SGML document type declaration,
<!DOCTYPE html>, which triggers the standards-compliant rendering mode. As of 5 January 2009, HTML5 also includes Web Forms 2.0, a previously separate WHATWG specification.New APIs
In addition to specifying markup, HTML5 specifies scripting application programming interfaces (APIs) that can be used with JavaScript.Existing document object model (DOM) interfaces are extended and de facto features documented. There are also new APIs, such as:
- The canvas element for immediate mode 2D drawing. See Canvas 2D API Specification 1.0 specification
- Timed media playback
- Offline Web Applications
- Document editing
- Drag-and-drop
- Cross-document messaging
- Browser history management
- MIME type and protocol handler registration
- Microdata
- Web Storage, a key-value pair storage framework that provides behaviour similar to cookies but with larger storage capacity and improved API.
Not all of the above technologies are included in the W3C HTML5 specification, though they are in the WHATWG HTML specification. Some related technologies, which are not part of either the W3C HTML5 or the WHATWG HTML specification, are as follows. The W3C publishes specifications for these separately:
- Geolocation
- Web SQL Database, a local SQL Database (no longer maintained).
- The Indexed Database API, an indexed hierarchical key-value store (formerly WebSimpleDB).
- HTML5 File API, handles file uploads and file manipulation.
- Directories and System, an API intended to satisfy client-side-storage use cases not well served by databases.
- File Writer, an API for writing to files from web applications.
- Web Audio API, a high-level JavaScript API for processing and synthesizing audio in web applications.
- ClassList API
HTML5 cannot provide animation within web pages. Additional JavaScript or CSS3 functionality is necessary for animating HTML elements. Animation is also possible using JavaScript and HTML and within SVG elements through SMIL, although browser support of the latter remains uneven as of 2011.
XHTML5 (XML-serialized HTML5)
XML documents must be served with an XML Internet media type (often called "MIME type") such as
application/xhtml+xml or application/xml, and must conform to strict, well-formed syntax of XML. XHTML5 is simply a XML-serialized HTML5 data (e.g. not having any unclosed tags), sent with one of XML media types. HTML that has been written to conform to both the HTML and XHTML specifications — and which will therefore produce the same DOM tree whether parsed as HTML or XML — is termed "polyglot markup".Error handling
HTML5 is designed so that old browsers can safely ignore new HTML5 constructs. In contrast to HTML 4.01, the HTML5 specification gives detailed rules for lexing and parsing, with the intent that different compliant browsers will produce the same result in the case of incorrect syntax.[57] Although HTML5 now defines a consistent behavior for "tag soup" documents, those documents are not regarded as conforming to the HTML5 standard.
Popularity
According to a report released on 30 September 2011, 34 of the world's top 100 Web sites were using HTML5 – the adoption led by search engines and social networks.]Another report released in August 2013 has shown that 153 of the Fortune 500 U.S. companies already implemented HTML5 on their corporate websites.
As of 2013, HTML 5 is at least partially supported by most popular layout engines.
Differences from HTML 4.01 and XHTML 1.x
The following is a cursory list of differences and some specific examples.
- New parsing rules: oriented towards flexible parsing and compatibility; not based on SGML
- Ability to use inline SVG and MathML in
text/html - New elements:
article,aside,audio,bdi,canvas,command,data,datalist,details,embed,figcaption,figure,footer,header,keygen,mark,meter,nav,output,progress,rp,rt,ruby,section,source,summary,time,track,video,wbr - New types of form controls:
dates and times,email,url,search,number,range,tel,color - New attributes:
charset(onmeta),async(onscript) - Global attributes (that can be applied for every element):
id,tabindex,hidden,data-*(custom data attributes) - Deprecated elements will be dropped altogether:
acronym,applet,basefont,big,center,dir,font,frame,frameset,isindex,noframes,strike,
dev.w3.org provides the latest Editors Draft of "HTML5 differences from HTML 4", which provides a complete outline of additions, removals and changes between HTML5 and HTML 4.
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