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 (RFC 1590) and MIME Content Type
(RFC 1521) 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
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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.
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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
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of the 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.
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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
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.
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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 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'.
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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.
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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.
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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.
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WWW
The World-Wide Web is a hypertext-based, distributed
information system created by researchers at CERN in
Switzerland.
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.
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For example, consider the following document:
Some text. *wow*
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, `*' 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
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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
| |
| \-
|
\-BODY
|
\-P
|
\-
|
\-"Some text. "
|
\-EM
| |
| \-
| |
| \-"*wow*"
| |
| \-
|
\-
Some of the elements are delimited explicitly by tags, while the
boundaries of others are inferred. The element contains a
element and aelement. The contains
This is a Heading
Some elements only have a start-tag without an end-tag. For example, to create a line break, use the `' tag. Additionally, the end tags of some other elements, such as Paragraph (`'), List Item (`
'), Definition Term (`'), and
Definition Description (`') 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, `<>'; 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, `
', `', and `' are equivalent, whereas `&' is different from `&'. In a start-tag, the element name must immediately follow the tag open delimiter `<'. Berners-Lee & Connolly Standards Track [Page 14] RFC 1866 Hypertext Markup Language - 2.0 November 1995 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, `' should be written `
is the element name, src is the attribute name, and `http://host/dir/file.gif' is the attribute value:
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 Tab LF Line Feed CR Carriage Return SP Space " " " Quotation mark & & & Ampersand Berners-Lee & Connolly Standards Track [Page 15] RFC 1866 Hypertext Markup Language - 2.0 November 1995 For 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:
Berners-Lee & Connolly Standards Track [Page 16] RFC 1866 Hypertext Markup Language - 2.0 November 1995 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. 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. This document type declaration also refers to the HTML DTD which appears in 9.1, "HTML DTD". 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. 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
First Header
This is a paragraph in the example HTML file. Keep in mind Berners-Lee & Connolly Standards Track [Page 17] RFC 1866 Hypertext Markup Language - 2.0 November 1995 that the title does not appear in the document text, but that the header (defined by H1) does.
- First item in an ordered list.
- Second item in an ordered list.
- Note that lists can be nested;
- Whitespace may be used to assist in reading the HTML source.
- Third item in an ordered list.
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. This sentence of the paragraph is emphasized. Note that the </P> end tag has been omitted.
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 Berners-Lee & Connolly Standards Track [Page 18] RFC 1866 Hypertext Markup Language - 2.0 November 1995 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
Be sure to read these bold instructions.