RFC1866 - Hypertext Markup Language - 2.0

Network Working Group T. Berners-Lee
Request for Comments: 1866 MIT/W3C
Category: Standards Track D. Connolly
November 1995
Hypertext Markup Language - 2.0
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Hypertext Markup Language (Html) is a simple markup language used
to create hypertext documents that are platform independent. HTML
documents are SGML documents with generic semantics that are
appropriate for representing information from a wide range of
domains. HTML markup can represent hypertext news, mail,
documentation, and hypermedia; menus of options; database query
results; simple strUCtured documents with in-lined graphics; and
hypertext views of existing bodies of information.
HTML has been in use by the World Wide Web (WWW) global information
initiative since 1990. This specification roughly corresponds to the
capabilities of HTML in common use prior to June 1994. HTML is an
application of ISO Standard 8879:1986 Information Processing Text and
Office Systems; Standard Generalized Markup Language (SGML).
The "text/html" Internet Media Type (RFC1590) and MIME Content Type
(RFC1521) is defined by this specification.
Table of Contents
1. Introduction ........................................... 2
1.1 Scope .................................................. 3
1.2 Conformance ............................................ 3
2. Terms .................................................. 6
3. HTML as an Application of SGML .........................10
3.1 SGML Documents .........................................10
3.2 HTML Lexical Syntax ................................... 12
3.3 HTML Public Text Identifiers .......................... 17
3.4 Example HTML Document ................................. 17
4. HTML as an Internet Media Type ........................ 18
4.1 text/html media type .................................. 18
4.2 HTML Document Representation .......................... 19
5. Document Structure .................................... 20
5.1 Document Element: HTML ................................ 21
5.2 Head: HEAD ............................................ 21
5.3 Body: BODY ............................................ 24
5.4 Headings: H1 ... H6 ................................... 24
5.5 Block Structuring Elements ............................ 25
5.6 List Elements ......................................... 28
5.7 Phrase Markup ......................................... 30
5.8 Line Break: BR ........................................ 34
5.9 Horizontal Rule: HR ................................... 34
5.10 Image: IMG ............................................ 34
6. Characters, Words, and Paragraphs ..................... 35
6.1 The HTML Document Character Set ....................... 36
7. Hyperlinks ............................................ 36
7.1 Accessing Resources ................................... 37
7.2 Activation of Hyperlinks .............................. 38
7.3 Simultaneous Presentation of Image Resources .......... 38
7.4 Fragment Identifiers .................................. 38
7.5 Queries and Indexes ................................... 39
7.6 Image Maps ............................................ 39
8. Forms ................................................. 40
8.1 Form Elements ......................................... 40
8.2 Form Submission ....................................... 45
9. HTML Public Text ...................................... 49
9.1 HTML DTD .............................................. 49
9.2 Strict HTML DTD ....................................... 61
9.3 Level 1 HTML DTD ...................................... 62
9.4 Strict Level 1 HTML DTD ............................... 63
9.5 SGML Declaration for HTML ............................. 64
9.6 Sample SGML Open Entity Catalog for HTML .............. 65
9.7 Character Entity Sets ................................. 66
10. Security Considerations ............................... 69
11. References ............................................ 69
12. Acknowledgments ....................................... 71
12.1 Authors" Addresses .................................... 71
13. The HTML Coded Character Set .......................... 72
14. Proposed Entities ..................................... 75
1. Introduction
The HyperText Markup Language (HTML) is a simple data format used to
create hypertext documents that are portable from one platform to
another. HTML documents are SGML documents with generic semantics
that are appropriate for representing information from a wide range
of domains.
As HTML is an application of SGML, this specification assumes a
working knowledge of [SGML].
1.1. Scope
HTML has been in use by the World-Wide Web (WWW) global information
initiative since 1990. Previously, informal documentation on HTML has
been available from a number of sources on the Internet. This
specification brings together, clarifies, and formalizes a set of
features that roughly corresponds to the capabilities of HTML in
common use prior to June 1994. A number of new features to HTML are
being proposed and eXPerimented in the Internet community.
This document thus defines a HTML 2.0 (to distinguish it from the
previous informal specifications). Future (generally upwardly
compatible) versions of HTML with new features will be released with
higher version numbers.
HTML is an application of ISO Standard 8879:1986, "Information
Processing Text and Office Systems; Standard Generalized Markup
Language" (SGML). The HTML Document Type Definition (DTD) is a formal
definition of the HTML syntax in terms of SGML.
This specification also defines HTML as an Internet Media
Type[IMEDIA] and MIME Content Type[MIME] called `text/html". As such,
it defines the semantics of the HTML syntax and how that syntax
should be interpreted by user agents.
1.2. Conformance
This specification governs the syntax of HTML documents and ASPects
of the behavior of HTML user agents.
1.2.1. Documents
A document is a conforming HTML document if:
* It is a conforming SGML document, and it conforms to the
HTML DTD (see 9.1, "HTML DTD").
NOTE - There are a number of syntactic idioms that
are not supported or are supported inconsistently in
some historical user agent implementations. These
idioms are identified in notes like this throughout
this specification.
* It conforms to the application conventions in this
specification. For example, the value of the HREF attribute
of the <A> element must conform to the URI syntax.
* Its document character set includes [ISO-8859-1] and
agrees with [ISO-10646]; that is, each code position listed
in 13, "The HTML Coded Character Set" is included, and each
code position in the document character set is mapped to the
same character as [ISO-10646] designates for that code
position.
NOTE - The document character set is somewhat
independent of the character encoding scheme used to
represent a document. For example, the `ISO-2022-JP"
character encoding scheme can be used for HTML
documents, since its repertoire is a subset of the
[ISO-10646] repertoire. The critical distinction is
that numeric character references agree with
[ISO-10646] regardless of how the document is
encoded.
1.2.2. Feature Test Entities
The HTML DTD defines a standard HTML document type and several
variations, by way of feature test entities. Feature test entities
are declarations in the HTML DTD that control the inclusion or
exclusion of portions of the DTD.
HTML.Recommended
Certain features of the language are necessary for
compatibility with widespread usage, but they may
compromise the structural integrity of a document. This
feature test entity selects a more prescriptive document
type definition that eliminates those features. It is
set to `IGNORE" by default.
For example, in order to preserve the structure of a
document, an editing user agent may translate HTML
documents to the recommended subset, or it may require
that the documents be in the recommended subset for
import.
HTML.Deprecated
Certain features of the language are necessary for
compatibility with earlier versions of the
specification, but they tend to be used and implemented
inconsistently, and their use is deprecated. This
feature test entity enables a document type definition
that allows these features. It is set to `INCLUDE" by
default.
Documents generated by translation software or editing
software should not contain deprecated idioms.
1.2.3. User Agents
An HTML user agent conforms to this specification if:
* It parses the characters of an HTML document into data
characters and markup according to [SGML].
NOTE - In the interest of robustness and
extensibility, there are a number of widely deployed
conventions for handling non-conforming documents.
See 4.2.1, "Undeclared Markup Error Handling" for
details.
* It supports the `ISO-8859-1" character encoding scheme and
processes each character in the ISO Latin Alphabet No. 1 as
specified in 6.1, "The HTML Document Character Set".
NOTE - To support non-western writing systems, HTML
user agents are encouraged to support
`ISO-10646-UCS-2" or similar character encoding
schemes and as much of the character repertoire of
[ISO-10646] as is practical.
* It behaves identically for documents whose parsed token
sequences are identical.
For example, comments and the whitespace in tags disappear
during tokenization, and hence they do not influence the
behavior of conforming user agents.
* It allows the user to traverse (or at least attempt to
traverse, resources permitting) all hyperlinks from <A>
elements in an HTML document.
An HTML user agent is a level 2 user agent if, additionally:
* It allows the user to express all form field values
specified in an HTML document and to (attempt to) submit the
values as requests to information services.
2. Terms
absolute URI
a URI in absolute form; for example, as per [URL]
anchor
one of two ends of a hyperlink; typically, a phrase
marked as an <A> element.
base URI
an absolute URI used in combination with a relative URI
to determine another absolute URI.
character
An atom of information, for example a letter or a digit.
Graphic characters have associated glyphs, whereas
control characters have associated processing semantics.
character encoding
scheme
A function whose domain is the set of sequences of
octets, and whose range is the set of sequences of
characters from a character repertoire; that is, a
sequence of octets and a character encoding scheme
determines a sequence of characters.
character repertoire
A finite set of characters; e.g. the range of a coded
character set.
code position
An integer. A coded character set and a code position
from its domain determine a character.
coded character set
A function whose domain is a subset of the integers and
whose range is a character repertoire. That is, for some
set of integers (usually of the form {0, 1, 2, ..., N}
), a coded character set and an integer in that set
determine a character. Conversely, a character and a
coded character set determine the character"s code
position (or, in rare cases, a few code positions).
conforming HTML user
agent
A user agent that conforms to this specification in its
processing of the Internet Media Type `text/html".
data character
Characters other than markup, which make up the content
of elements.
document character set
a coded character set whose range includes all
characters used in a document. Every SGML document has
exactly one document character set. Numeric character
references are resolved via the document character set.
DTD
document type definition. Rules that apply SGML to the
markup of documents of a particular type, including a
set of element and entity declarations. [SGML]
element
A component of the hierarchical structure defined by a
document type definition; it is identified in a document
instance by descriptive markup, usually a start-tag and
end-tag. [SGML]
end-tag
Descriptive markup that identifies the end of an
element. [SGML]
entity
data with an associated notation or interpretation; for
example, a sequence of octets associated with an
Internet Media Type. [SGML]
fragment identifier
the portion of an HREF attribute value following the `#"
character which modifies the presentation of the
destination of a hyperlink.
form data set
a sequence of name/value pairs; the names are given by
an HTML document and the values are given by a user.
HTML document
An SGML document conforming to this document type
definition.
hyperlink
a relationship between two anchors, called the head and
the tail. The link goes from the tail to the head. The
head and tail are also known as destination and source,
respectively.
markup
Syntactically delimited characters added to the data of
a document to represent its structure. There are four
different kinds of markup: descriptive markup (tags),
references, markup declarations, and processing
instructions. [SGML]
may
A document or user interface is conforming whether this
statement applies or not.
media type
an Internet Media Type, as per [IMEDIA].
message entity
a head and body. The head is a collection of name/value
fields, and the body is a sequence of octets. The head
defines the content type and content transfer encoding
of the body. [MIME]
minimally conforming
HTML user agent
A user agent that conforms to this specification except
for form processing. It may only process level 1 HTML
documents.
must
Documents or user agents in conflict with this statement
are not conforming.
numeric character
reference
markup that refers to a character by its code position
in the document character set.
SGML document
A sequence of characters organized physically as a set
of entities and logically into a hierarchy of elements.
An SGML document consists of data characters and markup;
the markup describes the structure of the information
and an instance of that structure. [SGML]
shall
If a document or user agent conflicts with this
statement, it does not conform to this specification.
should
If a document or user agent conflicts with this
statement, undesirable results may occur in practice
even though it conforms to this specification.
start-tag
Descriptive markup that identifies the start of an
element and specifies its generic identifier and
attributes. [SGML]
syntax-reference
character set
A coded character set whose range includes all
characters used for markup; e.g. name characters and
delimiter characters.
tag
Markup that delimits an element. A tag includes a name
which refers to an element declaration in the DTD, and
may include attributes. [SGML]
text entity
A finite sequence of characters. A text entity typically
takes the form of a sequence of octets with some
associated character encoding scheme, transmitted over
the network or stored in a file. [SGML]
typical
Typical processing is described for many elements. This
is not a mandatory part of the specification but is
given as guidance for designers and to help explain the
uses for which the elements were intended.
URI
A Uniform Resource Identifier is a formatted string that
serves as an identifier for a resource, typically on the
Internet. URIs are used in HTML to identify the anchors
of hyperlinks. URIs in common practice include Uniform
Resource Locators (URLs)[URL] and Relative URLs
[RELURL].
user agent
A component of a distributed system that presents an
interface and processes requests on behalf of a user;
for example, a www browser or a mail user agent.
WWW
The World-Wide Web is a hypertext-based, distributed
information system created by researchers at CERN in
Switzerland. <URL:http://www.w3.org/>
3. HTML as an Application of SGML
HTML is an application of ISO 8879:1986 -- Standard Generalized
Markup Language (SGML). SGML is a system for defining structured
document types and markup languages to represent instances of those
document types[SGML]. The public text -- DTD and SGML declaration --
of the HTML document type definition are provided in 9, "HTML Public
Text".
The term "HTML" refers to both the document type defined here and the
markup language for representing instances of this document type.
3.1. SGML Documents
An HTML document is an SGML document; that is, a sequence of
characters organized physically into a set of entities, and logically
as a hierarchy of elements.
In the SGML specification, the first production of the SGML syntax
grammar separates an SGML document into three parts: an SGML
declaration, a prologue, and an instance. For the purposes of this
specification, the prologue is a DTD. This DTD describes another
grammar: the start symbol is given in the doctype declaration, the
terminals are data characters and tags, and the productions are
determined by the element declarations. The instance must conform to
the DTD, that is, it must be in the language defined by this grammar.
The SGML declaration determines the lexicon of the grammar. It
specifies the document character set, which determines a character
repertoire that contains all characters that occur in all text
entities in the document, and the code positions associated with
those characters.
The SGML declaration also specifies the syntax-reference character
set of the document, and a few other parameters that bind the
abstract syntax of SGML to a concrete syntax. This concrete syntax
determines how the sequence of characters of the document is mapped
to a sequence of terminals in the grammar of the prologue.
For example, consider the following document:
<!DOCTYPE html PUBLIC "-//IETF//DTD HTML 2.0//EN">
<title>Parsing Example</title>
<p>Some text. <em>&#42;wow&#42;</em></p>
An HTML user agent should use the SGML declaration that is given in
9.5, "SGML Declaration for HTML". According to its document character
set, `&#42;" refers to an asterisk character, `*".
The instance above is regarded as the following sequence of
terminals:
1. start-tag: TITLE
2. data characters: "Parsing Example"
3. end-tag: TITLE
4. start-tag: P
5. data characters "Some text."
6. start-tag: EM
7. data characters: "*wow*"
8. end-tag: EM
9. end-tag: P
The start symbol of the DTD grammar is HTML, and the productions are
given in the public text identified by `-//IETF//DTD HTML 2.0//EN"
(9.1, "HTML DTD"). The terminals above parse as:
HTML

-HEAD

-TITLE

-<TITLE>

-"Parsing Example"

-</TITLE>

-BODY

-P

-<P>

-"Some text. "

-EM

-<EM>

-"*wow*"

-</EM>

-</P>
Some of the elements are delimited explicitly by tags, while the
boundaries of others are inferred. The <HTML> element contains a
<HEAD> element and a <BODY> element. The <HEAD> contains <TITLE>,
which is explicitly delimited by start- and end-tags.
3.2. HTML Lexical Syntax
SGML specifies an abstract syntax and a reference concrete syntax.
Aside from certain quantities and capacities (e.g. the limit on the
length of a name), all HTML documents use the reference concrete
syntax. In particular, all markup characters are in the repertoire of
[ISO-646]. Data characters are drawn from the document character set
(see 6, "Characters, Words, and Paragraphs").
A complete discussion of SGML parsing, e.g. the mapping of a sequence
of characters to a sequence of tags and data, is left to the SGML
standard[SGML]. This section is only a summary.
3.2.1. Data Characters
Any sequence of characters that do not constitute markup (see 9.6
"Delimiter Recognition" of [SGML]) are mapped directly to strings of
data characters. Some markup also maps to data character strings.
Numeric character references map to single-character strings, via the
document character set. Each reference to one of the general entities
defined in the HTML DTD maps to a single-character string.
For example,
abc&lt;def => "abc","<","def"
abc&#60;def => "abc","<","def"
The terminating semicolon on entity or numeric character references
is only necessary when the character following the reference would
otherwise be recognized as part of the name (see 9.4.5 "Reference
End" in [SGML]).
abc &lt def => "abc ","<"," def"
abc &#60 def => "abc ","<"," def"
An ampersand is only recognized as markup when it is followed by a
letter or a `#" and a digit:
abc & lt def => "abc & lt def"
abc &# 60 def => "abc &# 60 def"
A useful technique for translating plain text to HTML is to replace
each "<", "&", and ">" by an entity reference or numeric character
reference as follows:
ENTITY NUMERIC
CHARACTER REFERENCE CHAR REF CHARACTER DESCRIPTION
--------- ---------- ----------- ---------------------
& &amp; &#38; Ampersand
< &lt; &#60; Less than
> &gt; &#62; Greater than
NOTE - There are SGML mechanisms, CDATA and RCDATA
declared content, that allow most `<", `>", and `&"
characters to be entered without the use of entity
references. Because these mechanisms tend to be used and
implemented inconsistently, and because they conflict
with techniques for reducing HTML to 7 bit ASCII for
transport, they are deprecated in this version of HTML.
See 5.5.2.1, "Example and Listing: XMP, LISTING".
3.2.2. Tags
Tags delimit elements such as headings, paragraphs, lists, character
highlighting, and links. Most HTML elements are identified in a
document as a start-tag, which gives the element name and attributes,
followed by the content, followed by the end tag. Start-tags are
delimited by `<" and `>"; end tags are delimited by `</" and `>". An
example is:
<H1>This is a Heading</H1>
Some elements only have a start-tag without an end-tag. For example,
to create a line break, use the `<BR>" tag. Additionally, the end
tags of some other elements, such as Paragraph (`</P>"), List Item
(`</LI>"), Definition Term (`</DT>"), and Definition Description
(`</DD>") elements, may be omitted.
The content of an element is a sequence of data character strings and
nested elements. Some elements, such as anchors, cannot be nested.
Anchors and character highlighting may be put inside other
constructs. See the HTML DTD, 9.1, "HTML DTD" for full details.
NOTE - The SGML declaration for HTML specifies SHORTTAG YES, which
means that there are other valid syntaxes for tags, such as NET
tags, `<EM/.../"; empty start tags, `<>"; and empty end-tags,
`</>". Until support for these idioms is widely deployed, their
use is strongly discouraged.
3.2.3. Names
A name consists of a letter followed by letters, digits, periods, or
hyphens. The length of a name is limited to 72 characters by the
`NAMELEN" parameter in the SGML declaration for HTML, 9.5, "SGML
Declaration for HTML". Element and attribute names are not case
sensitive, but entity names are. For example, `<BLOCKQUOTE>",
`<BlockQuote>", and `<blockquote>" are equivalent, whereas `&amp;" is
different from `&AMP;".
In a start-tag, the element name must immediately follow the tag open
delimiter `<".
3.2.4. Attributes
In a start-tag, white space and attributes are allowed between the
element name and the closing delimiter. An attribute specification
typically consists of an attribute name, an equal sign, and a value,
though some attribute specifications may be just a name token. White
space is allowed around the equal sign.
The value of the attribute may be either:
* A string literal, delimited by single quotes or double
quotes and not containing any occurrences of the delimiting
character.
NOTE - Some historical implementations consider any
occurrence of the `>" character to signal the end of
a tag. For compatibility with such implementations,
when `>" appears in an attribute value, it should be
represented with a numeric character reference. For
example, `<IMG SRC="http://www.QQread.com/net-protocol/eq1.jpg" alt="a>b">" should be
written `<IMG SRC="http://www.qqread.com/net-protocol/eq1.jpg" alt="a&#62;b">" or `<IMG
SRC="http://www.qqread.com/net-protocol/eq1.jpg" alt="a&gt;b">".
* A name token (a sequence of letters, digits, periods, or
hyphens). Name tokens are not case sensitive.
NOTE - Some historical implementations allow any
character except space or `>" in a name token.
In this example, <img> is the element name, src is the attribute
name, and `http://host/dir/file.gif" is the attribute value:
<img src=http://host/dir/file.gif>
A useful technique for computing an attribute value literal for a
given string is to replace each quote and white space character by an
entity reference or numeric character reference as follows:
ENTITY NUMERIC
CHARACTER REFERENCE CHAR REF CHARACTER DESCRIPTION
--------- ---------- ----------- ---------------------
HT &#9; Tab
LF &#10; Line Feed
CR &#13; Carriage Return
SP &#32; Space
" &quot; &#34; Quotation mark
& &amp; &#38; Ampersand
For example:
<IMG SRC="http://www.qqread.com/net-protocol/image.jpg" alt="First &quot;real&quot; example">
The `NAMELEN" parameter in the SGML declaration (9.5, "SGML
Declaration for HTML") limits the length of an attribute value to
1024 characters.
Attributes such as ISMAP and COMPACT may be written using a minimized
syntax (see 7.9.1.2 "Omitted Attribute Name" in [SGML]). The markup:
<UL COMPACT="compact">
can be written using a minimized syntax:
<UL COMPACT>
NOTE - Some historical implementations only understand the minimized
syntax.
3.2.5. Comments
To include comments in an HTML document, use a comment declaration. A
comment declaration consists of `<!" followed by zero or more
comments followed by `>". Each comment starts with `--" and includes
all text up to and including the next occurrence of `--". In a
comment declaration, white space is allowed after each comment, but
not before the first comment. The entire comment declaration is
ignored.
NOTE - Some historical HTML implementations incorrectly consider
any `>" character to be the termination of a comment.
For example:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HEAD>
<TITLE>HTML Comment Example</TITLE>
<!-- Id: html-sgml.sgm,v 1.5 1995/05/26 21:29:50 connolly Exp -->
<!-- another -- -- comment -->
<!>
</HEAD>
<BODY>
<p> <!- not a comment, just regular old data characters ->
3.3. HTML Public Text Identifiers
To identify information as an HTML document conforming to this
specification, each document must start with one of the following
document type declarations.
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
This document type declaration refers to the HTML DTD in 9.1, "HTML
DTD".
NOTE - If the body of a `text/html" message entity does not begin
with a document type declaration, an HTML user agent should infer
the above document type declaration.
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Level 2//EN">
This document type declaration also refers to the HTML DTD which
appears in 9.1, "HTML DTD".
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Level 1//EN">
This document type declaration refers to the level 1 HTML DTD in 9.3,
"Level 1 HTML DTD". Form elements must not occur in level 1
documents.
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Strict//EN">
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Strict Level 1//EN">
These two document type declarations refer to the HTML DTD in 9.2,
"Strict HTML DTD" and 9.4, "Strict Level 1 HTML DTD". They refer to
the more structurally rigid definition of HTML.
HTML user agents may support other document types. In particular,
they may support other formal public identifiers, or other document
types altogether. They may support an internal declaration subset
with supplemental entity, element, and other markup declarations.
3.4. Example HTML Document
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HTML>
<!-- Here"s a good place to put a comment. -->
<HEAD>
<TITLE>Structural Example</TITLE>
</HEAD><BODY>
<H1>First Header</H1>
<P>This is a paragraph in the example HTML file. Keep in mind
that the title does not appear in the document text, but that
the header (defined by H1) does.</P>
<OL>
<LI>First item in an ordered list.
<LI>Second item in an ordered list.
<UL COMPACT>
<LI> Note that lists can be nested;
<LI> Whitespace may be used to assist in reading the
HTML source.
</UL>
<LI>Third item in an ordered list.
</OL>
<P>This is an additional paragraph. Technically, end tags are
not required for paragraphs, although they are allowed. You can
include character highlighting in a paragraph. <EM>This sentence
of the paragraph is emphasized.</EM> Note that the &lt;/P&gt;
end tag has been omitted.
<P>
<IMG SRC ="triangle.xbm" alt="Warning: ">
Be sure to read these <b>bold instructions</b>.
</BODY></HTML>
4. HTML as an Internet Media Type
An HTML user agent allows users to interact with resources which have
HTML representations. At a minimum, it must allow users to examine
and navigate the content of HTML level 1 documents. HTML user agents
should be able to preserve all formatting distinctions represented in
an HTML document, and be able to simultaneously present resources
referred to by IMG elements (they may ignore some formatting
distinctions or IMG resources at the request of the user). Level 2
HTML user agents should support form entry and submission.
4.1. text/html media type
This specification defines the Internet Media Type [IMEDIA] (formerly
referred to as the Content Type [MIME]) called `text/html". The
following is to be registered with [IANA].
Media Type name
text
Media suBType name
html
Required parameters
none
Optional parameters
level, charset
Encoding considerations
any encoding is allowed
Security considerations
see 10, "Security Considerations"
The optional parameters are defined as follows:
Level
The level parameter specifies the feature set used in
the document. The level is an integer number, implying
that any features of same or lower level may be present
in the document. Level 1 is all features defined in this
specification except those that require the <FORM>
element. Level 2 includes form processing. Level 2 is
the default.
Charset
The charset parameter (as defined in section 7.1.1 of
RFC1521[MIME]) may be given to specify the character
encoding scheme used to represent the HTML document as a
sequence of octets. The default value is outside the
scope of this specification; but for example, the
default is `US-ASCII" in the context of MIME mail, and
`ISO-8859-1" in the context of HTTP [HTTP].
4.2. HTML Document Representation
A message entity with a content type of `text/html" represents an
HTML document, consisting of a single text entity. The `charset"
parameter (whether implicit or explicit) identifies a character
encoding scheme. The text entity consists of the characters
determined by this character encoding scheme and the octets of the
body of the message entity.
4.2.1. Undeclared Markup Error Handling
To facilitate experimentation and interoperability between
implementations of various versions of HTML, the installed base of
HTML user agents supports a superset of the HTML 2.0 language by
reducing it to HTML 2.0: markup in the form of a start-tag or end-
tag, whose generic identifier is not declared is mapped to nothing
during tokenization. Undeclared attributes are treated similarly. The
entire attribute specification of an unknown attribute (i.e., the
unknown attribute and its value, if any) should be ignored. On the
other hand, references to undeclared entities should be treated as
data characters.
For example:
<div class=chapter><h1>foo</h1><p>...</div>
=> <H1>,"foo",</H1>,<P>,"..."
xxx <P ID=z23> yyy
=> "xxx ",<P>," yyy
Let &alpha; &amp; &beta; be finite sets.
=> "Let &alpha; & &beta; be finite sets."
Support for notifying the user of such errors is encouraged.
Information providers are warned that this convention is not binding:
unspecified behavior may result, as such markup does not conform to
this specification.
4.2.2. Conventional Representation of Newlines
SGML specifies that a text entity is a sequence of records, each
beginning with a record start character and ending with a record end
character (code positions 10 and 13 respectively) (section 7.6.1,
"Record Boundaries" in [SGML]).
[MIME] specifies that a body of type `text/*" is a sequence of lines,
each terminated by CRLF, that is, octets 13, 10.
In practice, HTML documents are frequently represented and
transmitted using an end of line convention that depends on the
conventions of the source of the document; frequently, that
representation consists of CR only, LF only, or a CR LF sequence.
Hence the decoding of the octets will often result in a text entity
with some missing record start and record end characters.
Since there is no ambiguity, HTML user agents are encouraged to infer
the missing record start and end characters.
An HTML user agent should treat end of line in any of its variations
as a word space in all contexts except preformatted text. Within
preformatted text, an HTML user agent should treat any of the three
common representations of end-of-line as starting a new line.
5. Document Structure
An HTML document is a tree of elements, including a head and body,
headings, paragraphs, lists, etc. Form elements are discussed in 8,
"Forms".
5.1. Document Element: HTML
The HTML document element consists of a head and a body, much like a
memo or a mail message. The head contains the title and optional
elements. The body is a text flow consisting of paragraphs, lists,
and other elements.
5.2. Head: HEAD
The head of an HTML document is an unordered collection of
information about the document. For example:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HEAD>
<TITLE>Introduction to HTML</TITLE>
</HEAD>
...
5.2.1. Title: TITLE
Every HTML document must contain a <TITLE> element.
The title should identify the contents of the document in a global
context. A short title, such as "Introduction" may be meaningless out
of context. A title such as "Introduction to HTML Elements" is more
appropriate.
NOTE - The length of a title is not limited; however, long titles
may be truncated in some applications. To minimize this
possibility, titles should be fewer than 64 characters.
A user agent may display the title of a document in a history list or
as a label for the window displaying the document. This differs from
headings (5.4, "Headings: H1 ... H6"), which are typically displayed
within the body text flow.
5.2.2. Base Address: BASE
The optional <BASE> element provides a base address for interpreting
relative URLs when the document is read out of context (see 7,
"Hyperlinks"). The value of the HREF attribute must be an absolute
URI.
5.2.3. Keyword Index: ISINDEX
The <ISINDEX> element indicates that the user agent should allow the
user to search an index by giving keywords. See 7.5, "Queries and
Indexes" for details.
5.2.4. Link: LINK
The <LINK> element represents a hyperlink (see 7, "Hyperlinks"). Any
number of LINK elements may occur in the <HEAD> element of an HTML
document. It has the same attributes as the <A> element (see 5.7.3,
"Anchor: A").
The <LINK> element is typically used to indicate authorship, related
indexes and glossaries, older or more recent versions, document
hierarchy, associated resources such as style sheets, etc.
5.2.5. Associated Meta-information: META
The <META> element is an extensible container for use in identifying
specialized document meta-information. Meta-information has two main
functions:
* to provide a means to discover that the data set exists
and how it might be obtained or accessed; and
* to document the content, quality, and features of a data
set, indicating its fitness for use.
Each <META> element specifies a name/value pair. If multiple META
elements are provided with the same name, their combined contents--
concatenated as a comma-separated list--is the value associated with
that name.
NOTE - The <META> element should not be used where a
specific element, such as <TITLE>, would be more
appropriate. Rather than a <META> element with a URI as
the value of the CONTENT attribute, use a <LINK>
element.
HTTP servers may read the content of the document <HEAD> to generate
header fields corresponding to any elements defining a value for the
attribute HTTP-EQUIV.
NOTE - The method by which the server extracts document
meta-information is unspecified and not mandatory. The
<META> element only provides an extensible mechanism for
identifying and embedding document meta-information --
how it may be used is up to the individual server
implementation and the HTML user agent.
Attributes of the META element:
HTTP-EQUIV
binds the element to an HTTP header field. An HTTP
server may use this information to process the document.
In particular, it may include a header field in the
responses to requests for this document: the header name
is taken from the HTTP-EQUIV attribute value, and the
header value is taken from the value of the CONTENT
attribute. HTTP header names are not case sensitive.
NAME
specifies the name of the name/value pair. If not
present, HTTP-EQUIV gives the name.
CONTENT
specifies the value of the name/value pair.
Examples
If the document contains:
<META HTTP-EQUIV="Expires"
CONTENT="Tue, 04 Dec 1993 21:29:02 GMT">
<meta http-equiv="Keywords" CONTENT="Fred">
<META HTTP-EQUIV="Reply-to"
content="fielding@ics.uci.edu (Roy Fielding)">
<Meta Http-equiv="Keywords" CONTENT="Barney">
then the server may include the following header fields:
Expires: Tue, 04 Dec 1993 21:29:02 GMT
Keywords: Fred, Barney
Reply-to: fielding@ics.uci.edu (Roy Fielding)
as part of the HTTP response to a `GET" or `HEAD" request for
that document.
An HTTP server must not use the <META> element to form an HTTP
response header unless the HTTP-EQUIV attribute is present.
An HTTP server may disregard any <META> elements that specify
information controlled by the HTTP server, for example `Server",
`Date", and `Last-modified".
5.2.6. Next Id: NEXTID
The <NEXTID> element is included for historical reasons only. HTML
documents should not contain <NEXTID> elements.
The <NEXTID> element gives a hint for the name to use for a new <A>
element when editing an HTML document. It should be distinct from all
NAME attribute values on <A> elements. For example:
<NEXTID N=Z27>
5.3. Body: BODY
The <BODY> element contains the text flow of the document, including
headings, paragraphs, lists, etc.
For example:
<BODY>
<h1>Important Stuff</h1>
<p>Explanation about important stuff...
</BODY>
5.4. Headings: H1 ... H6
The six heading elements, <H1> through <H6>, denote section headings.
Although the order and occurrence of headings is not constrained by
the HTML DTD, documents should not skip levels (for example, from H1
to H3), as converting such documents to other representations is
often problematic.
Example of use:
<H1>This is a heading</H1>
Here is some text
<H2>Second level heading</H2>
Here is some more text.
Typical renderings are:
H1
Bold, very-large font, centered. One or two blank lines
above and below.
H2
Bold, large font, flush-left. One or two blank lines
above and below.
H3
Italic, large font, slightly indented from the left
margin. One or two blank lines above and below.
H4
Bold, normal font, indented more than H3. One blank line
above and below.
H5
Italic, normal font, indented as H4. One blank line
above.
H6
Bold, indented same as normal text, more than H5. One
blank line above.
5.5. Block Structuring Elements
Block structuring elements include paragraphs, lists, and block
quotes. They must not contain heading elements, but they may contain
phrase markup, and in some cases, they may be nested.
5.5.1. Paragraph: P
The <P> element indicates a paragraph. The exact indentation, leading
space, etc. of a paragraph is not specified and may be a function of
other tags, style sheets, etc.
Typically, paragraphs are surrounded by a vertical space of one line
or half a line. The first line in a paragraph is indented in some
cases.
Example of use:
<H1>This Heading Precedes the Paragraph</H1>
<P>This is the text of the first paragraph.
<P>This is the text of the second paragraph. Although you do not
need to start paragraphs on new lines, maintaining this
convention facilitates document maintenance.</P>
<P>This is the text of a third paragraph.</P>
5.5.2. Preformatted Text: PRE
The <PRE> element represents a character cell block of text and is
suitable for text that has been formatted for a monospaced font.
The <PRE> tag may be used with the optional WIDTH attribute. The
WIDTH attribute specifies the maximum number of characters for a line
and allows the HTML user agent to select a suitable font and
indentation.
Within preformatted text:
* Line breaks within the text are rendered as a move to the
beginning of the next line.
NOTE - References to the "beginning of a new line"
do not imply that the renderer is forbidden from
using a constant left indent for rendering
preformatted text. The left indent may be
constrained by the width required.
* Anchor elements and phrase markup may be used.
NOTE - Constraints on the processing of <PRE>
content may limit or prevent the ability of the HTML
user agent to faithfully render phrase markup.
* Elements that define paragraph formatting (headings,
address, etc.) must not be used.
NOTE - Some historical documents contain <P> tags in
<PRE> elements. User agents are encouraged to treat
this as a line break. A <P> tag followed by a
newline character should produce only one line
break, not a line break plus a blank line.
* The horizontal tab character (code position 9 in the HTML
document character set) must be interpreted as the smallest
positive nonzero number of spaces which will leave the
number of characters so far on the line as a multiple of 8.
Documents should not contain tab characters, as they are not
supported consistently.
Example of use:
<PRE>
Line 1.
Line 2 is to the right of line 1. <a href="abc">abc</a>
Line 3 aligns with line 2. <a href="def">def</a>
</PRE>
5.5.2.1. Example and Listing: XMP, LISTING
The <XMP> and <LISTING> elements are similar to the <PRE> element,
but they have a different syntax. Their content is declared as CDATA,
which means that no markup except the end-tag open delimiter-in-
context is recognized (see 9.6 "Delimiter Recognition" of [SGML]).
NOTE - In a previous draft of the HTML specification, the syntax
of <XMP> and <LISTING> elements allowed closing tags to be treated
as data characters, as long as the tag name was not <XMP> or
<LISTING>, respectively.
Since CDATA declared content has a number of unfortunate interactions
with processing techniques and tends to be used and implemented
inconsistently, HTML documents should not contain <XMP> nor <LISTING>
elements -- the <PRE> tag is more expressive and more consistently
supported.
The <LISTING> element should be rendered so that at least 132
characters fit on a line. The <XMP> element should be rendered so
that at least 80 characters fit on a line but is otherwise identical
to the <LISTING> element.
NOTE - In a previous draft, HTML included a <PLAINTEXT> element
that is similar to the <LISTING> element, except that there is no
closing tag: all characters after the <PLAINTEXT> start-tag are
data.
5.5.3. Address: ADDRESS
The <ADDRESS> element contains such information as address, signature
and authorship, often at the beginning or end of the body of a
document.
Typically, the <ADDRESS> element is rendered in an italic typeface
and may be indented.
Example of use:
<ADDRESS>
Newsletter editor<BR>
J.R. Brown<BR>
JimquickPost News, Jimquick, CT 01234<BR>
Tel (123) 456 7890
</ADDRESS>
5.5.4. Block Quote: BLOCKQUOTE
The <BLOCKQUOTE> element contains text quoted from another source.
A typical rendering might be a slight extra left and right indent,
and/or italic font. The <BLOCKQUOTE> typically provides space above
and below the quote.
Single-font rendition may reflect the quotation style of Internet
mail by putting a vertical line of graphic characters, such as the
greater than symbol (>), in the left margin.
Example of use:
I think the play ends
<BLOCKQUOTE>
<P>Soft you now, the fair Ophelia. Nymph, in thy orisons, be all
my sins remembered.
</BLOCKQUOTE>
but I am not sure.
5.6. List Elements
HTML includes a number of list elements. They may be used in
combination; for example, a <OL> may be nested in an <LI> element of
a <UL>.
The COMPACT attribute suggests that a compact rendering be used.
5.6.1. Unordered List: UL, LI
The <UL> represents a list of items -- typically rendered as a
bulleted list.
The content of a <UL> element is a sequence of <LI> elements. For
example:
<UL>
<LI>First list item
<LI>Second list item
<p>second paragraph of second item
<LI>Third list item
</UL>
5.6.2. Ordered List: OL
The <OL> element represents an ordered list of items, sorted by
sequence or order of importance. It is typically rendered as a
numbered list.
The content of a <OL> element is a sequence of <LI> elements. For
example:
<OL>
<LI>Click the Web button to open URI window.
<LI>Enter the URI number in the text field of the Open URI
window. The Web document you specified is displayed.
<ol>
<li>substep 1
<li>substep 2
</ol>
<LI>Click highlighted text to move from one link to another.
</OL>
5.6.3. Directory List: DIR
The <DIR> element is similar to the <UL> element. It represents a
list of short items, typically up to 20 characters each. Items in a
directory list may be arranged in columns, typically 24 characters
wide.
The content of a <DIR> element is a sequence of <LI> elements.
Nested block elements are not allowed in the content of <DIR>
elements. For example:
<DIR>
<LI>A-H<LI>I-M
<LI>M-R<LI>S-Z
</DIR>
5.6.4. Menu List: MENU
The <MENU> element is a list of items with typically one line per
item. The menu list style is typically more compact than the style of
an unordered list.
The content of a <MENU> element is a sequence of <LI> elements.
Nested block elements are not allowed in the content of <MENU>
elements. For example:
<MENU>
<LI>First item in the list.
<LI>Second item in the list.
<LI>Third item in the list.
</MENU>
5.6.5. Definition List: DL, DT, DD
A definition list is a list of terms and corresponding definitions.
Definition lists are typically formatted with the term flush-left and
the definition, formatted paragraph style, indented after the term.
The content of a <DL> element is a sequence of <DT> elements and/or
<DD> elements, usually in pairs. Multiple <DT> may be paired with a
single <DD> element. Documents should not contain multiple
consecutive <DD> elements.
Example of use:
<DL>
<DT>Term<DD>This is the definition of the first term.
<DT>Term<DD>This is the definition of the second term.
</DL>
If the DT term does not fit in the DT column (typically one third of
the display area), it may be extended across the page with the DD
section moved to the next line, or it may be wrapped onto successive
lines of the left hand column.
The optional COMPACT attribute suggests that a compact rendering be
used, because the list items are small and/or the entire list is
large.
Unless the COMPACT attribute is present, an HTML user agent may leave
white space between successive DT, DD pairs. The COMPACT attribute
may also reduce the width of the left-hand (DT) column.
<DL COMPACT>
<DT>Term<DD>This is the first definition in compact format.
<DT>Term<DD>This is the second definition in compact format.
</DL>
5.7. Phrase Markup
Phrases may be marked up according to idiomatic usage, typographic
appearance, or for use as hyperlink anchors.
User agents must render highlighted phrases distinctly from plain
text. Additionally, <EM> content must be rendered as distinct from
<STRONG> content, and <B> content must rendered as distinct from <I>
content.
Phrase elements may be nested within the content of other phrase
elements; however, HTML user agents may render nested phrase elements
indistinctly from non-nested elements:
plain <B>bold <I>italic</I></B> may be rendered
the same as plain <B>bold </B><I>italic</I>
5.7.1. Idiomatic Elements
Phrases may be marked up to indicate certain idioms.
NOTE - User agents may support the <DFN> element, not included in
this specification, as it has been deployed to some extent. It is
used to indicate the defining instance of a term, and it is
typically rendered in italic or bold italic.
5.7.1.1. Citation: CITE
The <CITE> element is used to indicate the title of a book or
other citation. It is typically rendered as italics. For example:
He just couldn"t get enough of <cite>The Grapes of Wrath</cite>.
5.7.1.2. Code: CODE
The <CODE> element indicates an example of code, typically
rendered in a mono-spaced font. The <CODE> element is intended for
short words or phrases of code; the <PRE> block structuring
element (5.5.2, "Preformatted Text: PRE") is more appropriate
for multiple-line listings. For example:
The expression <code>x += 1</code>
is short for <code>x = x + 1</code>.
5.7.1.3. Emphasis: EM
The <EM> element indicates an emphasized phrase, typically
rendered as italics. For example:
A singular subject <em>always</em> takes a singular verb.
5.7.1.4. Keyboard: KBD
The <KBD> element indicates text typed by a user, typically
rendered in a mono-spaced font. This is commonly used in
instruction manuals. For example:
Enter <kbd>FIND IT</kbd> to search the database.
5.7.1.5. Sample: SAMP
The <SAMP> element indicates a sequence of literal characters,
typically rendered in a mono-spaced font. For example:
The only word containing the letters <samp>mt</samp> is dreamt.
5.7.1.6. Strong Emphasis: STRONG
The <STRONG> element indicates strong emphasis, typically rendered
in bold. For example:
<strong>STOP</strong>, or I"ll say "<strong>STOP</strong>" again!
5.7.1.7. Variable: VAR
The <VAR> element indicates a placeholder variable, typically
rendered as italic. For example:
Type <SAMP>html-check <VAR>file</VAR> more</SAMP>
to check <VAR>file</VAR> for markup errors.
5.7.2. Typographic Elements
Typographic elements are used to specify the format of marked
text.
Typical renderings for idiomatic elements may vary between user
agents. If a specific rendering is necessary -- for example, when
referring to a specific text attribute as in "The italic parts are
mandatory" -- a typographic element can be used to ensure that the
intended typography is used where possible.
NOTE - User agents may support some typographic elements not
included in this specification, as they have been deployed to some
extent. The <STRIKE> element indicates horizontal line through the
characters, and the <U> element indicates an underline.
5.7.2.1. Bold: B
The <B> element indicates bold text. Where bold typography is
unavailable, an alternative representation may be used.
5.7.2.2. Italic: I
The <I> element indicates italic text. Where italic typography is
unavailable, an alternative representation may be used.
5.7.2.3. Teletype: TT
The <TT> element indicates teletype (monospaced )text. Where a
teletype font is unavailable, an alternative representation may be
used.
5.7.3. Anchor: A
The <A> element indicates a hyperlink anchor (see 7, "Hyperlinks").
At least one of the NAME and HREF attributes should be present.
Attributes of the <A> element:
HREF
gives the URI of the head anchor of a hyperlink.
NAME
gives the name of the anchor, and makes it available as
a head of a hyperlink.
TITLE
suggests a title for the destination resource --
advisory only. The TITLE attribute may be used:
* for display prior to accessing the destination
resource, for example, as a margin note or on a
small box while the mouse is over the anchor, or
while the document is being loaded;
* for resources that do not include a title, such as
graphics, plain text and Gopher menus, for use as a
window title.
REL
The REL attribute gives the relationship(s) described by
the hyperlink. The value is a whitespace separated list
of relationship names. The semantics of link
relationships are not specified in this document.
REV
same as the REL attribute, but the semantics of the
relationship are in the reverse direction. A link from A
to B with REL="X" expresses the same relationship as a
link from B to A with REV="X". An anchor may have both
REL and REV attributes.
URN
specifies a preferred, more persistent identifier for
the head anchor of the hyperlink. The syntax and
semantics of the URN attribute are not yet specified.
METHODS
specifies methods to be used in accessing the
destination, as a whitespace-separated list of names.
The set of applicable names is a function of the scheme
of the URI in the HREF attribute. For similar reasons as
for the TITLE attribute, it may be useful to include the
information in advance in the link. For example, the
HTML user agent may chose a different rendering as a
function of the methods allowed; for example, something
that is searchable may get a different icon.
5.8. Line Break: BR
The <BR> element specifies a line break between words (see 6,
"Characters, Words, and Paragraphs"). For example:
<P> Pease porridge hot<BR>
Pease porridge cold<BR>
Pease porridge in the pot<BR>
Nine days old.
5.9. Horizontal Rule: HR
The <HR> element is a divider between sections of text; typically a
full width horizontal rule or equivalent graphic. For example:
<HR>
<ADDRESS>February 8, 1995, CERN</ADDRESS>
</BODY>
5.10. Image: IMG
The <IMG> element refers to an image or icon via a hyperlink (see
7.3, "Simultaneous Presentation of Image Resources").
HTML user agents may process the value of the ALT attribute as an
alternative to processing the image resource indicated by the SRC
attribute.
NOTE - Some HTML user agents can process graphics linked via
anchors, but not <IMG> graphics. If a graphic is essential, it
should be referenced from an <A> element rather than an <IMG>
element. If the graphic is not essential, then the <IMG> element
is appropriate.
Attributes of the <IMG> element:
ALIGN
alignment of the image with respect to the text
baseline.
* `TOP" specifies that the top of the image aligns
with the tallest item on the line containing the
image.
* `MIDDLE" specifies that the center of the image
aligns with the baseline of the line containing the
image.
* `BOTTOM" specifies that the bottom of the image
aligns with the baseline of the line containing the
image.
ALT
text to use in place of the referenced image resource,
for example due to processing constraints or user
preference.
ISMAP
indicates an image map (see 7.6, "Image Maps").
SRC
specifies the URI of the image resource.
NOTE - In practice, the media types of image
resources are limited to a few raster graphic
formats: typically `image/gif", `image/jpeg". In
particular, `text/html" resources are not
intended to be used as image resources.
Examples of use:
<IMG SRC="triangle.xbm" ALT="Warning:"> Be sure
to read these instructions.
<a href="http://machine/htbin/imagemap/sample">
<IMG SRC="sample.xbm" ISMAP>
</a>
6. Characters, Words, and Paragraphs
An HTML user agent should present the body of an HTML document as a
collection of typeset paragraphs and preformatted text. Except for
preformatted elements (<PRE>, <XMP>, <LISTING>, <TEXTAREA>), each
block structuring element is regarded as a paragraph by taking the
data characters in its content and the content of its descendant
elements, concatenating them, and splitting the result into words,
separated by space, tab, or record end characters (and perhaps hyphen
characters). The sequence of words is typeset as a paragraph by
breaking it into lines.
6.1. The HTML Document Character Set
The document character set specified in 9.5, "SGML Declaration for
HTML" must be supported by HTML user agents. It includes the graphic
characters of Latin Alphabet No. 1, or simply Latin-1. Latin-1
comprises 191 graphic characters, including the alphabets of most
Western European languages.
NOTE - Use of the non-breaking space and soft hyphen indicator
characters is discouraged because support for them is not widely
deployed.
NOTE - To support non-western writing systems, a larger character
repertoire will be specified in a futu