To the extent possible under law, the editors have waived all copyright and related or neighboring rights to this work. In addition, as of 14 August 2016, the editors have made this specification available under the Open Web Foundation Agreement Version 1.0, which is available at http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0.
"Differences from HTML4" describes the differences of the HTML specification from those of HTML4.
This document covers the WHATWG HTML standard. It does not cover the W3C HTML5 or W3C HTML5.1 specifications. [HTML] [HTML5] [HTML5NIGHTLY]
HTML has been in continuous evolution since it was introduced to the Internet in the early 1990s. Some features were introduced in specifications; others were introduced in software releases. In some respects, implementations and Web developer practices have converged with each other and with specifications and standards, but in other ways, they have diverged.
The HTML specification reflects an effort, started in 2004, to study contemporary HTML implementations and Web content. The specification:
Defines a single language called HTML which can be written in HTML syntax and in XML syntax.
Defines detailed processing models to foster interoperable implementations.
Improves markup for documents.
Introduces markup and APIs for emerging idioms, such as Web applications.
See open issues in Bugzilla. The specification also has annotation boxes in the margin which can link to bugs.
HTML is defined in a way that is backward compatible with the way user agents handle content. To keep the language relatively simple for Web developers, several older elements and attributes are not included, as outlined in the other sections of this document, such as presentational elements that are better handled using CSS.
User agents, however, will always have to support these older
elements and attributes. This is why the HTML specification clearly
separates requirements for Web developers (referred to as "authors" in the
specification) and user agents; for instance, this
means that Web developers cannot use the
isindex or the
plaintext element, but user agents are required to support
them in a way that is compatible with how these elements need to behave
for compatibility with Web content.
Since HTML has separate conformance requirements for Web developers and user agents there is no longer a need for marking features "deprecated".
The HTML4 specification reached Recommendation status before it was completely implemented in user agents. HTML4 still is not completely implemented, because it contains various bugs that have been fixed in the current HTML specification, which user agents are much closer to implementing than HTML4.
The HTML standard is under continual development where bugs are fixed and new features are introduced over time. Features can also be removed from the specification if they lack implementor interest, are not being used by Web developers, or for other reasons.
HTML defines a syntax, referred to as "the HTML syntax", that is
mostly compatible with HTML4 and XHTML1 documents published on the
Web, but is not compatible with the more esoteric SGML features of
HTML4, such as
as these are not supported by most user agents. Documents using the HTML
syntax are served with the
HTML also defines detailed parsing rules (including "error
handling") for this syntax which are largely compatible with HTML4-era
implementations. User agents have to use these rules for resources that
text/html media type. Here is an example document
that conforms to the HTML syntax:
<!doctype html> <html> <head> <meta charset="UTF-8"> <title>Example document</title> </head> <body> <p>Example paragraph</p> </body> </html>
The other syntax that can be used for HTML is XML. This syntax
is compatible with XHTML1 documents and implementations. Documents
using this syntax need to be served with an XML media type (such as
application/xml) and elements
need to be put in the
namespace following the rules set forth by the XML specifications.
Below is an example document that conforms to the XML syntax of HTML.
<?xml version="1.0" encoding="UTF-8"?> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Example document</title> </head> <body> <p>Example paragraph</p> </body> </html>
For the HTML syntax, Web developers are required to declare the character encoding. There are three ways to do that:
At the transport level; for instance, by using the HTTP
Using a Unicode Byte Order Mark (BOM) character at the start of the file. This character provides a signature for the encoding used.
meta element with a
attribute that specifies the encoding within the first 1024 bytes of
the document; for instance,
could be used to specify the UTF-8 encoding. This replaces the need
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
although that syntax is still allowed.
For the XML syntax, Web developers have to use the rules as set forth in the XML specification to set the character encoding.
The HTML syntax requires a doctype to be specified to ensure that the browser renders the page in standards mode. The doctype has no other purpose. [DOCTYPE]
In HTML4, it was possible to use doctypes that were syntactically correct
but still trigger quirks mode (e.g.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">, without the URL).
If you were using no doctype or a quirky doctype and switch to a standards mode doctype, you will most likely run into differences between the modes. For example, in quirks mode, classes and IDs in Selectors are case-insensitive and CSS <length>s do not require a unit. For more examples, please refer to What happens in Quirks Mode?.
The doctype declaration for the HTML syntax is
<!DOCTYPE html> and is
case-insensitive. Doctypes from earlier versions of
HTML were longer because the HTML language was SGML-based and therefore
required a reference to a DTD. This is no longer the case and
the doctype is only needed to enable standards mode for documents
written using the HTML syntax. Browsers already do this for
To support legacy markup generators that cannot generate the preferred
short doctype, the doctype
<!DOCTYPE html SYSTEM
"about:legacy-compat"> is allowed in the HTML syntax.
The strict doctypes for HTML 4.0, HTML 4.01, XHTML 1.0 as well as XHTML 1.1 are also allowed (but are discouraged) in the HTML syntax.
In the XML syntax, any doctype declaration may be used, or it may be omitted altogether. Documents with an XML media type are always handled in standards mode.
The HTML syntax allows for MathML and SVG elements to
be used inside a document. An
tag causes the HTML parser to switch to a special insertion mode which puts
elements and attributes in the appropriate namespaces, does case fixups for
elements and attributes that have mixed case, and supports the empty-element
syntax as in XML. The syntax is still case-insensitive and attributes allow
the same syntax as for HTML elements. Namespace declarations may be omitted.
CDATA sections are supported in this insertion mode.
Some MathML and SVG elements cause the parser to switch back to "HTML
foreignObject, so you can
use HTML elements or a new
For instance, a very simple document using some of the minimal syntax features could look like:
<!doctype html> <title>SVG in text/html</title> <p> A green circle: <svg> <circle r="50" cx="50" cy="50" fill="green"/> </svg> </p>
There are a few other changes in the HTML syntax worthy of mentioning:
⟩ named character references now expand to U+27E8 and U+27E9 (mathematical left/right angle
bracket) instead of U+2329 and U+232A (left/right-pointing angle bracket), respectively.
Many new named character references have been added, including all named character references from MathML.
Void elements (known as "EMPTY" in HTML4) are allowed to have a trailing slash.
The ampersand (
&) may be left unescaped in more
cases compared to HTML4.
Attributes have to be separated by at least one whitespace character.
Attributes with an empty value may be written as just the attribute name omitting the equals sign and the value, even if the attribute is not a boolean attribute. (It is commonly believed that HTML4 allowed the value to be omitted for boolean attributes. Instead, HTML4 allowed using only the attribute value and omitting the attribute name, for enumerated attributes, but this was not supported in browsers.)
Attributes omitting quotes for the value are allowed to use a larger set of characters compared to HTML4.
The HTML parser does not do any normalization of whitespace in attribute values; for instance, leading and trailing whitespace in the
id attribute is not ignored (and thus now invalid), and newline characters can be used in the
value attribute of the
input element without using character
optgroup end tag is now optional.
colgroup start tag is now optional and is inferred by
the HTML parser.
This section is split up in several subsections to more clearly illustrate the various differences from HTML4.
The following elements have been introduced for better structure:
represents an independent piece of content of a document, such as a
blog entry or newspaper article.
can be used as a container for the dominant contents of another element, such as
the main content of the page.
represents a piece of content that is only slightly related to the
rest of the page.
represents the header of a section.
represents a group of introductory or navigational aids.
represents a footer for a section and can contain information about
the author, copyright information, etc.
represents a section of the document intended for navigation.
represents a piece of self-contained flow content, typically
referenced as a single unit from the main flow of the document.
<figure> <video src="example.webm" controls></video> <figcaption>Example</figcaption> </figure>
figcaption can be used as caption (it is optional).
can be used to declare fragments of HTML that can be cloned and inserted in the document by script.
Then there are several other new elements:
audio for multimedia content. Both
provide an API so application Web developers can script their own user
interface, but there is also a way to trigger a user interface
provided by the user agent.
elements are used together with these elements if there are multiple
streams available of different types.
embed is used for plugin
mark represents a run of
text in one document marked or highlighted for reference purposes, due
to its relevance in another context.
progress represents a
completion of a task, such as downloading or when performing a series
of expensive operations.
meter represents a
measurement, such as disk usage.
time represents a date
allows content to be annotated with a machine-readable value.
dialog for showing a dialog.
bdi represents a span of
text that is to be isolated from its surroundings for the purposes of
bidirectional text formatting.
wbr represents a line break
canvas is used for rendering
dynamic bitmap graphics on the fly, such as graphs or games.
represents a command the user can invoke from a popup menu.
<input list="browsers"> <datalist id="browsers"> <option value="Safari"> <option value="Internet Explorer"> <option value="Opera"> <option value="Firefox"> </datalist>
represents control for key pair generation.
represents some type of output, such as from a calculation done
type attribute now has the
following new values:
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.
Several attributes have been introduced to various elements that were already part of HTML4:
autofocus attribute can be specified on the
input (except when the
type attribute is
button elements. It provides a declarative way to focus a
form control during page load. Using this feature should enhance the
user experience compared to focusing the element with script as the user can turn it off if the user does not like
it, for instance.
<input type=search name=q placeholder="Enter search phrase..."> <button>Search</button>
<label>Email <input type=email name=email placeholder="firstname.lastname@example.org"></label>
<!-- Do not do this: --> <input type=email name=email placeholder="Email">
form attribute for
fieldset elements allows for
controls to be associated with a form. These elements can now be
placed anywhere on a page, not just as descendants of the
form element, and still be associated with a
<table> <tr> <th>Key <th>Value <th>Action <tr> <td><form id=1><input name=1-key></form> <td><input form=1 name=1-value> <td><button form=1 name=1-action value=save>✓</button> <button form=1 name=1-action value=delete>✗</button> ... </table>
required attribute applies to
input (except when the
type attribute is
image or some button type such as
textarea. It indicates that the user
has to fill in a value in order to submit the form. For
select, the first
option element has to be a placeholder with an empty value.
<label>Color: <select name=color required> <option value="">Choose one <option>Red <option>Green <option>Blue </select></label>
fieldset element now allows the
disabled attribute which disables all descendant controls (excluding those that are descendants of the
when specified, and the
name attribute which can be used for script access.
input element has several new attributes to
step. As mentioned before it also has a new
list attribute which can be used together with the
datalist element. It also now has the
height attributes to specify the dimensions of the image when using
button elements have
formtarget as new attributes. If present, they override
target attributes on the
menu element has two new attributes:
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
link element has a new attribute called
sizes. It can be used in conjunction with the
icon relationship (set through the
attribute; can be used for e.g. favicons) to indicate the size of the
referenced icon, thus allowing for icons of distinct dimensions.
img element has a new attribute called
crossorigin to use CORS in the fetch and if it is successful, allows the image data to be
read with the
script element has a
crossorigin attribute to allow script
errors to be reported to
onerror with information about the error.
link element also has a
img element has new attributes called
along with the new elements
to allow Web developers to declaratively control or give hints to the user agent
about which image resource to use, based on the screen pixel density,
viewport size, image format, and other factors.
Several attributes from HTML4 now apply to all elements. These
are called global attributes:
title. Additionally, XHTML 1.0
xml:space on some elements, which is now allowed
on all elements in XHTML documents.
There are also several new global attributes:
contenteditable attribute indicates that
the element is an editable area. The user can change the contents of the
element and manipulate the markup.
contextmenu attribute can be used to point
to a context menu provided by the Web developer.
data-* collection of Web developer-defined
attributes. Web developers can define any attribute they want as long as they
prefix it with
data- to avoid clashes with future versions of
HTML. These are intended to be used to store custom data to be consumed by
the Web page or application itself. They are not intended for
data to be consumed by other parties (e.g. user agents).
attribute indicates that an element is not yet, or is no longer, relevant.
spellcheck attribute allows for hinting
whether content can be checked for spelling or not.
translate attribute gives a hint to
translators whether the content should be translated.
HTML also makes all event handler attributes from HTML4, which take the
onevent, global attributes and adds
several new event handler attributes for new events it defines; for
event handler attribute for the
play event which is used by the API for the
media elements (
The specification has an index of all events.
These elements have slightly modified meanings in HTML to better reflect how they are used on the Web or to make them more useful:
b element now represents a
span of text to which attention is being drawn for utilitarian purposes
without conveying any extra importance and with no implication of an
alternate voice or mood, such as key words in a document abstract, product
names in a review, actionable words in interactive text-driven software,
or an article lede.
cite element now solely
represents the title of a work (e.g. a book, a paper, an essay, a poem, a
score, a song, a script, a film, a TV show, a game, a sculpture, a
painting, a theatre production, a play, an opera, a musical, an
exhibition, a legal case report, etc). Specifically the example in HTML4
where it is used to mark up the name of a person is no longer considered
dl element now represents an
association list of name-value groups, and is no longer said to be
appropriate for dialogue.
hr element now represents a
paragraph-level thematic break.
i element now represents a
span of text in an alternate voice or mood, or otherwise offset from the
normal prose in a manner indicating a different quality of text, such as a
taxonomic designation, a technical term, an idiomatic phrase from another
language, a thought, or a ship name in Western texts.
label element the
browser should no longer move focus from the label to the control unless
such behavior is standard for the underlying platform user
menu element is redefined to
be useful for toolbars and popup menus.
s element now represents
contents that are no longer accurate or no longer relevant.
script element can now be
used for scripts or for custom data blocks.
small element now represents
side comments such as small print.
strong element now
represents importance rather than strong emphasis.
u element now represents a
span of text with an unarticulated, though explicitly rendered,
non-textual annotation, such as labeling the text as being a proper name
in Chinese text (a Chinese proper name mark), or labeling the text as
Several attributes have changed in various ways.
accesskey global attribute now allows multiple
characters to be specified, which the user agent can choose from.
attribute now allows the value
object are no longer allowed to contain
percentages. They are also not allowed to be used to stretch the image to
a different aspect ratio than its intrinsic aspect ratio.
attribute is now allowed to have any value, as long as it is unique, is
not the empty string, and does not contain space characters.
attribute takes the empty string in addition to a valid language
identifier, just like
xml:lang does in XML.
The event handler attributes (e.g.
global attribute now always uses CSS as the styling language.
global attribute now allows negative values which indicate that the
element can receive focus but cannot be tabbed to.
The elements in this section are not to be used by Web developers. User
agents will still have to support them and various sections in
HTML define how. E.g. the obsolete
is handled by the parser section.
The following elements are not in HTML because their effect is purely presentational and their function is better handled by CSS:
The following elements are not in HTML because using them damages usability and accessibility:
The following elements are not included because they have not been used often, created confusion, or their function can be handled by other elements:
isindex usage can be replaced by usage of form controls.
noscript element is only conforming in the
HTML syntax. It is not allowed in the XML syntax. This is because in order to not only hide visually but also prevent the content to run scripts, apply style sheets, have submittable form controls, load resources, and so forth, the HTML parser parses the content of the
noscript element as plain text. The same is not possible with an XML parser.
Some attributes from HTML4 are no longer allowed in HTML. The specification defines how user agents should process them in legacy documents, but Web developers are not allowed use them and they will not validate.
HTML has advice on what you can use instead.
In addition, HTML has none of the presentational attributes that were in HTML4 as their functions are better handled by CSS:
The following attributes are allowed but Web developers are discouraged from using them and instead strongly encouraged to use an alternative solution:
language attribute on
script. It is required to have the value
conflict with the
type attribute. Web developers can simply omit it as
it has no useful function.
The content model is what defines how elements may be nested — what is allowed as children (or descendants) of a certain element.
At a high level, HTML4 had two major categories of elements, "inline"
img, text), and "block-level" (e.g.
table). Some elements did not fit in
Some elements allowed "inline" elements (e.g.
p), some allowed "block-level" elements (e.g.
body), some allowed both (e.g.
div), while other elements did not allow either
category but only allowed other specific elements (e.g.
or did not allow any children at all (e.g.
Notice the difference between an element itself being in a
certain category, and having a content model of a certain category; for
p element is itself a
"block-level" element, but has a content model of "inline".
To make it more confusing, HTML4 had different content model rules in its
Strict, Transitional and Frameset flavors; for instance, in Strict, the
body element allowed only "block-level"
elements, but in Transitional, it allowed both "inline" and "block-level".
To make things more confusing still, CSS uses the terms "block-level element" and "inline-level element" for its visual formatting model, which is related to CSS's 'display' property and has nothing to do with HTML's content model rules.
HTML does not use the terms "block-level" or "inline" as part of its content model rules, to reduce confusion with CSS. However, it has more categories than HTML4, and an element can be part of none of them, one of them, or several of them.
Heading content, e.g.
As a broad change from HTML4, HTML no longer has any element that only
accepts what HTML4 called "block-level" elements; e.g. the
body element now allows flow content. Thus, This is
closer to HTML4 Transitional than HTML4 Strict.
Further changes include:
noscript element was a
"block-level" element in HTML4, but is phrasing content in HTML.
Table elements have to conform to the table model (e.g. two cells are not allowed to overlap).
a element now has a transparent content model (except it does not
allow interactive content descendants), meaning that it has the same
content model as its parent. This means that the
a element can now contain e.g.
div elements, if its parent allows flow
map element also has a
transparent content model. The
element is considered phrasing content if there is a
map element ancestor, which means that they
do not need to be direct children of
HTML has introduced many new APIs and has extended, changed or obsoleted some existing APIs.
HTML introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications:
An API for form constraint validation (e.g. the
An API for commands that the user can invoke.
An API that enables offline Web applications, with an application cache.
Editing API in combination with a new global
Drag & drop API in combination with a
An API that exposes the components of the document's URL and allows
scripts to navigate, redirect and reload (the
An API that exposes the session history and allows scripts to
update the document's URL without actually navigating, so that
applications don't need to abuse the fragment component for "Ajax-style"
An API for printing the document (
An API for microdata.
An API for bidirectional client-server communication (
An API for server-to-client data push (
The following features from DOM Level 2 HTML are changed in various ways:
document.title now collapses whitespace on
document.domain is made settable, which
can change the document's effective script origin.
document.open() now either clears the
document (if invoked with two or less arguments), or acts like
window.open() (if invoked with
three or four arguments). In the former case, throws an exception in XML.
document.writeln() throw an exception in
XML. The latter two now support variadic arguments; they can add text to
the document's input stream while it is still being parsed, imply a
document.open(), or be ignored altogether in
now returns all HTML elements with a
name attribute matching
DOM Level 2 HTML had an
HTMLDocument interface that
Document and provided HTML-specific members on
documents. HTML has moved these members to the
Document interface, and extended it in a number
of ways. Since all documents use the
Document interface, the
HTML-specific members are now available on all documents, so they are usable
in e.g. SVG documents as well. It also has several new members:
getItems() for microdata.
to accompany the CSS
Existing scripts that modified the prototype of
should continue to work because
window.HTMLDocument now returns
Document interface object.
HTMLElement interface has also gained several extensions
dataset is a
convenience feature for handling the
data-* attributes, which are exposed as
camel-cased properties; for instance,
= 'test' sets the
data-foo-bar content attribute on
isContentEditable returns true if the
element is editable.
forceSpellCheck() causes the user agent to check spelling of an element.
All event handler IDL attributes.
Some members were previously defined on
HTMLElement but been moved to the
interface in the DOM standard: [DOM]
id reflects the
id content attribute.
className reflects the
class content attribute.
getElementsByClassName() returns a list of elements with the specified
Some interfaces in DOM Level 2 HTML have been extended.
HTMLSelectElement now has a
namedItem() methods, a setter creator,
labels IDL attributes,
and members for the form constrain validation API:
HTMLInputElement now has the
stepDown(), the form
constraint validation API members,
labels, and members for the text field selection
HTMLAnchorElement now has the
text, and implements the
URLUtils interface which has the members
HTMLAreaElement also have the
relList IDL attribute.
HTMLAreaElement also implements the
In addition, most new content attributes also have corresponding IDL
attributes on the elements' interfaces, e.g. the
sizes IDL attribute on
HTMLLinkElement which reflects the
sizes content attribute.
Some APIs are now either removed altogether, or marked as obsolete.
All IDL attributes that reflect a content attribute that is itself
obsolete, are now also obsolete; for instance, the
bgColor IDL attribute on
HTMLBodyElement which reflects the
content attribute is now obsolete.
The following interfaces are marked obsolete since the elements are
HTMLIsIndexElement interface is removed altogether since
the HTML parser expands an
isindex tag into other elements. The
HTMLBaseFontElement interface is also removed since the element has no effect.
The following members of the
HTMLDocument interface (which
have now moved to
Document) are now
The editors would like to thank Ben Millard, Bruce Lawson, Cameron McCormack, Charles McCathieNevile, Dan Connolly, David Håsäther, Dennis German, Frank Ellermann, Frank Palinkas, 羽田野太巳 (Futomi Hatano), Gordon P. Hemsley, Henri Sivonen, Jacob Palme, James Graham, Jens Oliver Meiert, Jeremy Keith, Jukka K. Korpela, Jürgen Jeka, Krijn Hoetmer, Leif Halvard Silli, Maciej Stachowiak, Mallory van Achterberg, Marcos Caceres, Mark Pilgrim, Martijn Wargers, Martin Leese, Martyn Haigh, Masataka Yakura, Michael Smith, Mike Taylor, Ms2ger, Olivier Gendrin, Øistein E. Andersen, Philip Jägenstedt, Philip Taylor, Randy Peterman, Robin Berjon, Steve Faulkner, Timo Tijhof, Toby Inkster, Xaxio Brandish, Yngve Spjeld Landro and Zhong Yu 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!