a declarative header section (delimited by the HEAD
element),
a body, which contains the document's actual content. The body may be
implemented by the BODY element or the
FRAMESET element.
White space (spaces, newlines, tabs, and comments) may appear before or
after each section. Sections 2 and 3 should be delimited by the HTML
element.
Here's an example of a simple HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>My first HTML document</TITLE>
</HEAD>
<BODY>
<P>Hello world!
</BODY>
</HTML>
A valid HTML document declares what version of HTML is used in the document.
The document type declaration
names the document type definition (DTD) in use for the document (see
[ISO8879]).
HTML 4.01 specifies three DTDs, so authors must include one of the following
document type declarations in their documents. The DTDs vary in the elements
they support.
The HTML 4.01 Strict DTD includes all elements and
attributes that have not been
deprecated or do not appear in frameset documents. For documents that use
this DTD, use this document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
The HTML 4.01
Transitional DTD includes everything in the strict DTD plus
deprecated elements and attributes (most of which concern visual presentation).
For documents that use this DTD, use this document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
The HTML 4.01 Frameset DTD includes
everything in the transitional DTD plus frames as well. For documents that use
this DTD, use this document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
The URI in each document type declaration allows user agents to download the
DTD and any entity sets that are
needed. The following (relative) URIs refer to DTDs and
entity sets for HTML 4:
The binding between public identifiers and files can be specified using a
catalog file following the format recommended by the Oasis Open Consortium (see
[OASISOPEN]). A sample catalog file
for HTML 4.01 is included at the beginning of the section on SGML reference
information for HTML. The last two letters of the declaration indicate the
language of the DTD. For HTML, this is always English ("EN").
Note. As of the 24 December version of HTML 4.01, the
HTML Working Group commits to the following policy:
Any changes to future HTML 4 DTDs will not invalidate documents that
conform to the DTDs of the present specification. The HTML Working Group
reserves the right to correct known bugs.
Software conforming to the DTDs of the present specification may ignore
features of future HTML 4 DTDs that it does not recognize.
This means that in a document type declaration, authors may safely use a
system identifier that refers to the latest version of an HTML 4 DTD. Authors
may also choose to use a system identifier that refers to a specific (dated)
version of an HTML 4 DTD when validation to that particular DTD is required.
W3C will make every effort to make archival documents indefinitely available at
their original address in their original form.
Deprecated. The
value of this attribute specifies which HTML DTD version governs the current
document. This attribute has been deprecated because it is redundant with version information provided by the document type
declaration.
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n; -- lang, dir --
profile%URI; #IMPLIED -- named dictionary of meta info --
>
This attribute specifies the location of one or more meta data profiles,
separated by white space. For future extensions, user agents should consider
the value to be a list even though this specification only considers the first
URI to be significant. Profiles are discussed below in
the section on meta data.
The
HEAD element contains information about the current document, such
as its title, keywords that may be useful to search engines, and other data
that is not considered document content. User agents do not generally render
elements that appear in the HEAD as content. They may, however, make
information in the HEAD available to users through other mechanisms.
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
Every HTML document must have a TITLE
element in the HEAD section.
Authors should use the TITLE element to identify the contents of a
document. Since users often consult documents out of context,
authors should provide context-rich titles. Thus, instead of a title such as
"Introduction", which doesn't provide much contextual background, authors
should supply a title such as "Introduction to Medieval Bee-Keeping"
instead.
For reasons of accessibility, user agents must always make the content of
the
TITLE element available to users (including TITLE
elements that occur in frames). The mechanism for doing so depends on the user
agent (e.g., as a caption, spoken).
Titles may contain character entities
(for accented characters, special characters, etc.), but may not contain other
markup (including comments). Here is a sample document title:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
... other head elements...
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
This attribute offers advisory information about the element for which it
is set.
Unlike the TITLE element, which provides information about an entire
document and may only appear once, the title attribute may annotate any number
of elements. Please consult an element's definition to
verify that it supports this attribute.
Values of the title attribute may be rendered by user agents in a variety
of ways. For instance, visual browsers frequently display the title as a "tool
tip" (a short message that appears when the pointing device pauses over an
object). Audio user agents may speak the title information in a similar
context. For example, setting the attribute on a link allows user agents
(visual and non-visual) to tell users about the nature of the linked
resource:
...some text...
Here's a photo of
<A href="http://someplace.com/neatstuff.gif" title="Me scuba diving">
me scuba diving last summer
</A>
...some more text...
Note. To improve the quality of speech synthesis for
cases handled poorly by standard techniques, future versions of HTML may
include an attribute for encoding phonemic and prosodic information.
Note. The W3C
Resource Description Framework (see [RDF10]) became a W3C
Recommendation in February 1999. RDF allows authors to specify machine-readable
metadata about HTML documents and other network-accessible resources.
HTML lets authors specify meta data -- information about a document rather
than document content -- in a variety of ways.
For example, to specify the author of a document, one may use the META
element as follows:
<META name="Author" content="Dave Raggett">
The
META element specifies a property (here "Author") and assigns a
value to it (here "Dave Raggett").
This specification does not define a set of legal meta data properties. The
meaning of a property and the set of legal values for that property should be
defined in a reference lexicon called a profile. For
example, a profile designed to help search engines index documents might define
properties such as "author", "copyright", "keywords", etc.
Specifying meta data
In general, specifying meta data involves two steps:
Declaring a property and a value for that property. This may be done in two
ways:
From outside a document, by linking to meta data via the LINK
element (see the section on link
types).
Referring to a profile where the property and its
legal values are defined. To designate a profile, use the
profile attribute of the HEAD element.
Note that since a profile is defined for the HEAD element, the same profile
applies to all META and LINK elements in the document head.
User agents are not required to support meta data mechanisms. For those that
choose to support meta data, this specification does not define how meta data
should be interpreted.
<!ELEMENT META - O EMPTY -- generic metainformation -->
<!ATTLIST META
%i18n; -- lang, dir, for use with content --
http-equivNAME #IMPLIED -- HTTP response header name --
nameNAME #IMPLIED -- metainformation name --
contentCDATA #REQUIRED -- associated information --
schemeCDATA #IMPLIED -- select form of content --
>
Start tag: required, End tag:
forbidden
Attribute definitions
For the following attributes, the permitted values and their interpretation
are
profile dependent:
The
META element can be used to identify properties of a document (e.g.,
author, expiration date, a list of key words, etc.) and assign values to those
properties. This specification does not define a normative set of
properties.
Each
META element specifies a property/value pair. The name attribute identifies the property and the
content attribute specifies the property's value.
For example, the following declaration sets a value for the Author
property:
<META name="Author" content="Dave Raggett">
The
lang attribute can be used with META to specify the language for
the value of the content attribute. This enables speech synthesizers to apply
language dependent pronunciation rules.
In this example, the author's name is declared to be French:
<META name="Author" lang="fr" content="Arnaud Le Hors">
Note. The META element is a generic mechanism for
specifying meta data. However, some HTML elements and attributes already handle
certain pieces of meta data and may be used by authors instead of META to
specify those pieces: the TITLE element, the ADDRESS element, the INS and DEL
elements, the title attribute, and the cite attribute.
Note. When a property specified by a META
element takes a value that is a URI, some
authors prefer to specify the meta data via the LINK
element. Thus, the following meta data declaration:
The http-equiv attribute can be used in place of the name attribute and has a special significance when
documents are retrieved via the Hypertext Transfer Protocol (HTTP). HTTP
servers may use the property name specified by the
http-equiv attribute to create an [RFC822]-style header in
the HTTP response. Please see the HTTP specification ([RFC2616]) for
details on valid HTTP headers.
<META http-equiv="Expires" content="Tue, 20 Aug 1996 14:25:27 GMT">
will result in the HTTP header:
Expires: Tue, 20 Aug 1996 14:25:27 GMT
This can be used by caches to determine when to fetch a fresh copy of the
associated document.
Note. Some user agents support the use of META to
refresh the current page after a specified number of seconds, with the option
of replacing it by a different URI. Authors should not use
this technique to forward users to different pages, as this makes the page
inaccessible to some users. Instead, automatic page forwarding should be done
using server-side redirects.
A common use for META is to specify keywords that a search
engine may use to improve the quality of search results. When
several
META elements provide language-dependent information about a
document, search engines may filter on the lang attribute to display search
results using the language preferences of the user. For example,
<-- For speakers of US English -->
<META name="keywords" lang="en-us"
content="vacation, Greece, sunshine">
<-- For speakers of British English -->
<META name="keywords" lang="en"
content="holiday, Greece, sunshine">
<-- For speakers of French -->
<META name="keywords" lang="fr"
content="vacances, Grèce, soleil">
The effectiveness of search engines can also be increased by using the LINK
element to specify links to translations of the document in other languages,
links to versions of the document in other media (e.g., PDF), and, when the
document is part of a collection, links to an appropriate starting point for
browsing the collection.
The Platform
for Internet Content Selection (PICS, specified in [PICS])
is an infrastructure for associating labels (meta data) with Internet content.
Originally designed to help parents and teachers control what children can
access on the Internet, it also facilitates other uses for labels, including
code signing, privacy, and intellectual property rights management.
This example illustrates how one can use a META declaration to include a
PICS 1.1 label:
<HEAD>
<META http-equiv="PICS-Label" content='
(PICS-1.1 "http://www.gcf.org/v2.5"
labels on "1994.11.05T08:15-0500"
until "1995.12.31T23:59-0000"
for "http://w3.org/PICS/Overview.html"
ratings (suds 0.5 density 0 color/hue 1))
'>
<TITLE>... document title ...</TITLE>
</HEAD>
The
profile attribute of the HEAD specifies the location of a meta data profile. The value of the
profile attribute is a URI. User agents may use this URI in two
ways:
As a globally unique name. User agents may be able to recognize the name
(without actually retrieving the profile) and perform some activity based on
known conventions for that profile. For instance, search engines could provide
an interface for searching through catalogs of HTML documents, where these
documents all use the same profile for representing catalog entries.
As a link. User agents may dereference the URI and perform some activity
based on the actual definitions within the profile (e.g., authorize the usage
of the profile within the current HTML document). This specification does not
define formats for profiles.
This example refers to a hypothetical profile that defines useful properties
for document indexing. The properties defined by this profile -- including
"author", "copyright", "keywords", and "date" -- have their values set by
subsequent
META declarations.
As this specification is being written, it is common practice to use the
date formats described in [RFC2616], section 3.3. As
these formats are relatively hard to process, we recommend that authors use the
[ISO8601] date format. For more information, see the sections on the INS and
DEL
elements.
The
scheme attribute allows authors to provide user agents more
context for the correct interpretation of meta data. At times, such
additional information may be critical, as when meta data may be specified in
different formats. For example, an author might specify a date in the
(ambiguous) format "10-9-97"; does this mean 9 October 1997 or 10 September
1997? The
scheme attribute value "Month-Day-Year" would disambiguate this date
value.
At other times, the scheme attribute may provide helpful but non-critical
information to user agents.
For example, the following scheme declaration may help a user agent
determine that the value of the "identifier" property is an ISBN code
number:
Values for the scheme attribute depend on the property
name and the associated profile.
Note. One sample profile is the Dublin Core (see
[DCORE]). This profile defines a set of recommended properties for
electronic bibliographic descriptions, and is intended to promote
interoperability among disparate description models.
The body of a document contains the document's content. The content may be
presented by a user agent in a variety of ways. For example, for visual
browsers, you can think of the body as a canvas where the content appears:
text, images, colors, graphics, etc. For audio user agents, the same content
may be spoken. Since style sheets are now
the preferred way to specify a document's presentation, the presentational
attributes of BODY have been
deprecated.
DEPRECATED EXAMPLE:
The following HTML fragment illustrates the use of the deprecated attributes. It sets the background
color of the canvas to white, the text foreground color to black, and the color
of hyperlinks to red initially, fuchsia when activated, and maroon once
visited.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
</HEAD>
<BODY bgcolor="white" text="black"
link="red" alink="fuchsia" vlink="maroon">
... document body...
</BODY>
</HTML>
Using style sheets, the same effect
could be accomplished as follows:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<STYLE type="text/css">
BODY { background: white; color: black}
A:link { color: red }
A:visited { color: maroon }
A:active { color: fuchsia }
</STYLE>
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
Using external (linked) style sheets gives you the flexibility to change the
presentation without revising the source HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<LINK rel="stylesheet" type="text/css" href="smartstyle.css">
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
This attribute assigns a class name or set of class names to an element.
Any number of elements may be assigned the same class name or names. Multiple
class names must be separated by white space characters.
The
id attribute assigns a unique
identifier to an element (which may be verified by an SGML parser).
For example, the following paragraphs are distinguished by their id values:
<P id="myparagraph"> This is a uniquely named paragraph.</P>
<P id="yourparagraph"> This is also a uniquely named paragraph.</P>
For general purpose processing by user agents (e.g. for identifying fields
when extracting data from HTML pages into a database, translating HTML
documents into other formats, etc.).
The
class attribute, on the other hand, assigns one or more class names
to an element; the element may be said to belong to these classes. A class name
may be shared by several element instances. The class
attribute has several roles in HTML:
As a style sheet selector (when an
author wishes to assign style information to a set of elements).
For general purpose processing by user agents.
In the following example, the SPAN
element is used in conjunction with the id and class attributes to markup
document messages. Messages appear in both English and French versions.
<!-- French messages -->
<P><SPAN id="msg1" class="info" lang="fr">Variable déclarée deux fois</SPAN>
<P><SPAN id="msg2" class="warning" lang="fr">Variable indéfinie</SPAN>
<P><SPAN id="msg3" class="error" lang="fr">Erreur de syntaxe pour variable</SPAN>
The following CSS style rules would tell visual user agents to display
informational messages in green, warning messages in yellow, and error messages
in red:
SPAN.info { color: green }
SPAN.warning { color: yellow }
SPAN.error { color: red }
Note that the French "msg1" and the English "msg1" may not appear in the
same document since they share the same id value. Authors may make further use
of the
id attribute to refine the presentation of individual messages, make
them target anchors, etc.
Almost every HTML element may be assigned identifier and class
information.
Suppose, for example, that we are writing a document about a programming
language. The document is to include a number of preformatted examples. We use
the
PRE element to format the examples. We also assign a background
color (green) to all instances of the PRE element belonging to the class
"example".
By setting the id attribute for this example, we can (1) create a hyperlink
to it and (2) override class style information with instance style
information.
Note. The id attribute shares the same name space as the
name attribute when used for anchor names. Please
consult the section on anchors with
id for more information.
Certain HTML elements that may appear in BODY are said to be "block-level" while others are
"inline" (also known as "text level"). The distinction is founded on
several notions:
Content model
Generally, block-level elements may contain inline elements and other
block-level elements. Generally, inline elements may contain only data and
other inline elements. Inherent in this structural distinction is the idea that
block elements create "larger" structures than inline elements.
Formatting
By default, block-level elements are formatted differently than inline
elements. Generally, block-level elements begin on new lines, inline elements
do not. For information about white space, line breaks, and block formatting,
please consult the section on text.
Directionality
For technical reasons involving the [UNICODE] bidirectional
text algorithm, block-level and inline elements differ in how they inherit
directionality information. For details, see the section on inheritance of text direction.
Style sheets provide the means to
specify the rendering of arbitrary elements, including whether an element is
rendered as block or inline. In some cases, such as an inline style for list
elements, this may be appropriate, but generally speaking, authors are
discouraged from overriding the conventional interpretation of HTML elements in
this way.
The
DIV and SPAN elements, in conjunction with the id and
class attributes, offer a generic mechanism for adding structure to
documents. These elements define content to be inline (SPAN) or
block-level (DIV) but impose no other presentational idioms on the
content. Thus, authors may use these elements in conjunction with style sheets, the lang attribute, etc., to tailor
HTML to their own needs and tastes.
Suppose, for example, that we wanted to generate an HTML document based on a
database of client information. Since HTML does not include elements that
identify objects such as "client", "telephone number", "email address", etc.,
we use
DIV and SPAN to achieve the desired structural and presentational
effects. We might use the TABLE element as follows to structure the
information:
A heading element briefly describes the topic of the section it introduces.
Heading information may be used by user agents, for example, to construct a
table of contents for a document automatically.
There are six levels of headings in HTML with H1 as the most important and H6 as
the least. Visual browsers usually render more important headings in larger
fonts than less important ones.
The following example shows how to use the DIV element to associate a
heading with the document section that follows it. Doing so allows you to
define a style for the section (color the background, set the font, etc.) with
style sheets.
<DIV class="section" id="forest-elephants" >
<H1>Forest elephants</H1>
<P>In this section, we discuss the lesser known forest elephants.
...this section continues...
<DIV class="subsection" id="forest-habitat" >
<H2>Habitat</H2>
<P>Forest elephants do not live in trees but among them.
...this subsection continues...
</DIV>
</DIV>
This structure may be decorated with style information such as:
Numbered sections and references
HTML does not itself cause section numbers
to be generated from headings. This facility may be offered by user agents,
however. Soon, style sheet languages such as CSS will allow authors to control
the generation of section numbers (handy for forward references in printed
documents, as in "See section 7.2").
Some people consider skipping heading levels to be bad
practice. They accept H1 H2 H1 while they do not accept H1 H3
H1 since the heading level H2 is skipped.
The
ADDRESS element may be used by authors to supply contact information
for a document or a major part of a document such as a form. This element often
appears at the beginning or end of a document.
For example, a page at the W3C Web site related to HTML might include the
following contact information:
<ADDRESS>
<A href="../People/Raggett/">Dave Raggett</A>,
<A href="../People/Arnaud/">Arnaud Le Hors</A>,
contact persons for the <A href="Activity">W3C HTML Activity</A><BR>
$Date: 1999/12/24 23:07:14 $
</ADDRESS>
