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>

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

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<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

--------- ---------- ----------- ---------------------

& & & Ampersand

< < < Less than

> > > 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 `&' 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>b">' or `<IMG

SRC="http://www.qqread.com/net-protocol/eq1.jpg" alt="a>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:

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

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:

can be written using a minimized syntax:

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>

<!>

</HEAD>

<BODY>

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>

<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.

<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 </P>

end tag has been omitted.

<P>

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:

=> <H1>,"foo",</H1>,<P>,"..."

xxx <P ID=z23> yyy

=> "xxx ",<P>," yyy

Let α & β be finite sets.

=> "Let α & β 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="Reply-to"

content="fielding@ics.uci.edu (Roy Fielding)">

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:

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:

Bold, very-large font, centered. One or two blank lines

above and below.

Bold, large font, flush-left. One or two blank lines

above and below.

Italic, large font, slightly indented from the left

margin. One or two blank lines above and below.

Bold, normal font, indented more than H3. One blank line

above and below.

Italic, normal font, indented as H4. One blank line

above.

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:

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

<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.

<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>

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 future version of HTML. The

document character set will be [ISO-10646], or some subset that

agrees with [ISO-10646]; in particular, all numeric character

references must use code positions assigned by [ISO-10646].

In SGML applications, the use of control characters is limited in

order to maximize the chance of successful interchange over

heterogeneous networks and operating systems. In the HTML document

character set only three control characters are allowed: Horizontal

Tab, Carriage Return, and Line Feed (code positions 9, 13, and 10).

The HTML DTD references the Added Latin 1 entity set, to allow

mnemonic representation of selected Latin 1 characters using only the

widely supported ASCII character repertoire. For example:

Kurt Gödel was a famous logician and mathematician.

See 9.7.2, "ISO Latin 1 Character Entity Set" for a table of the

"Added Latin 1" entities, and 13, "The HTML Coded Character Set" for

a table of the code positions of [ISO 8859-1] and the control

characters in the HTML document character set.

7. Hyperlinks

In addition to general purpose elements such as paragraphs and lists,

HTML documents can express hyperlinks. An HTML user agent allows the

user to navigate these hyperlinks.

A hyperlink is a relationship between two anchors, called the head

and the tail of the hyperlink[DEXTER]. Anchors are identified by an

anchor address: an absolute Uniform Resource Identifier (URI),

optionally followed by a '#' and a sequence of characters called a

fragment identifier. For example:

http://www.w3.org/hypertext/WWW/TheProject.html

http://www.w3.org/hypertext/WWW/TheProject.html#z31

In an anchor address, the URI refers to a resource; it may be used in

a variety of information retrieval protocols to obtain an entity that

represents the resource, such as an HTML document. The fragment

identifier, if present, refers to some view on, or portion of the

resource.

Each of the following markup constructs indicates the tail anchor of

a hyperlink or set of hyperlinks:

* <A> elements with HREF present.

* <LINK> elements.

* <IMG> elements.

* <INPUT> elements with the SRC attribute present.

* <ISINDEX> elements.

* <FORM> elements with `METHOD=GET'.

These markup constructs refer to head anchors by a URI, either

absolute or relative, or a fragment identifier, or both.

In the case of a relative URI, the absolute URI in the address of the

head anchor is the result of combining the relative URI with a base

absolute URI as in [RELURL]. The base document is taken from the

document's <BASE> element, if present; else, it is determined as in

[RELURL].

7.1. Accessing Resources

Once the address of the head anchor is determined, the user agent may

obtain a representation of the resource.

For example, if the base URI is `http://host/x/y.html' and the

document contains:

then the user agent uses the URI `http://host/icons/abc.gif' to

access the resource, as in [URL]..

7.2. Activation of Hyperlinks

An HTML user agent allows the user to navigate the content of the

document and request activation of hyperlinks denoted by <A>

elements. HTML user agents should also allow activation of <LINK>

element hyperlinks.

To activate a link, the user agent obtains a representation of the

resource identified in the address of the head anchor. If the

representation is another HTML document, navigation may begin again

with this new document.

7.3. Simultaneous Presentation of Image Resources

An HTML user agent may activate hyperlinks indicated by <IMG> and

<INPUT> elements concurrently with processing the document; that is,

image hyperlinks may be processed without explicit request by the

user. Image resources should be embedded in the presentation at the

point of the tail anchor, that is the <IMG> or <INPUT> element.

<LINK> hyperlinks may also be processed without explicit user

request; for example, style sheet resources may be processed before

or during the processing of the document.

7.4. Fragment Identifiers

Any characters following a `#' character in a hypertext address

constitute a fragment identifier. In particular, an address of the

form `#fragment' refers to an anchor in the same document.

The meaning of fragment identifiers depends on the media type of the

representation of the anchor's resource. For `text/html'

representations, it refers to the <A> element with a NAME attribute

whose value is the same as the fragment identifier. The matching is

case sensitive. The document should have exactly one such element.

The user agent should indicate the anchor element, for example by

scrolling to and/or highlighting the phrase.

For example, if the base URI is `http://host/x/y.html' and the user

activated the link denoted by the following markup:

<p> See: <a href="app1.html#bananas">appendix 1</a>

for more detail on bananas.

Then the user agent accesses the resource identified by

`http://host/x/app1.html'. Assuming the resource is represented using

the `text/html' media type, the user agent must locate the <A>

element whose NAME attribute is `bananas' and begin navigation there.

7.5. Queries and Indexes

The <ISINDEX> element represents a set of hyperlinks. The user can

choose from the set by providing keywords to the user agent. The

user agent computes the head URI by appending `?' and the keywords to

the base URI. The keywords are escaped according to [URL] and joined

by `+'. For example, if a document contains:

and the user provides the keywords `apple' and `berry', then the

user agent must access the resource

`http://host/index?apple+berry'.

<FORM> elements with `METHOD=GET' also represent sets of

hyperlinks. See 8.2.2, "Query Forms: METHOD=GET" for details.

7.6. Image Maps

If the ISMAP attribute is present on an <IMG> element, the <IMG>

element must be contained in an <A> element with an HREF present.

This construct represents a set of hyperlinks. The user can choose

from the set by choosing a pixel of the image. The user agent

computes the head URI by appending `?' and the x and y coordinates of

the pixel to the URI given in the <A> element. For example, if a

document contains:

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">

<head><title>ImageMap Example</title>

<body>

<p> Choose any of these icons:<br>

and the user chooses the upper-leftmost pixel, the chosen

hyperlink is the one with the URI

`http://host/cgi-bin/imagemap?0,0'.

8. Forms

A form is a template for a form data set and an associated

method and action URI. A form data set is a sequence of

name/value pair fields. The names are specified on the NAME

attributes of form input elements, and the values are given

initial values by various forms of markup and edited by the

user. The resulting form data set is used to access an

information service as a function of the action and method.

Forms elements can be mixed in with document structuring

elements. For example, a <PRE> element may contain a <FORM>

element, or a <FORM> element may contain lists which contain

<INPUT> elements. This gives considerable flexibility in

designing the layout of forms.

Form processing is a level 2 feature.

8.1. Form Elements

8.1.1. Form: FORM

The <FORM> element contains a sequence of input elements, along

with document structuring elements. The attributes are:

ACTION

specifies the action URI for the form. The action URI of

a form defaults to the base URI of the document (see 7,

"Hyperlinks").

METHOD

selects a method of accessing the action URI. The set of

applicable methods is a function of the scheme of the

action URI of the form. See 8.2.2, "Query Forms:

METHOD=GET" and 8.2.3, "Forms with Side-Effects:

METHOD=POST".

ENCTYPE

specifies the media type used to encode the name/value

pairs for transport, in case the protocol does not

itself impose a format. See 8.2.1, "The form-urlencoded

Media Type".

8.1.2. Input Field: INPUT

The <INPUT> element represents a field for user input. The TYPE

attribute discriminates between several variations of fields.

The <INPUT> element has a number of attributes. The set of applicable

attributes depends on the value of the TYPE attribute.

8.1.2.1. Text Field: INPUT TYPE=TEXT

The default value of the TYPE attribute is `TEXT', indicating a

single line text entry field. (Use the <TEXTAREA> element for multi-

line text fields.)

Required attributes are:

NAME

name for the form field corresponding to this element.

The optional attributes are:

MAXLENGTH

constrains the number of characters that can be entered

into a text input field. If the value of MAXLENGTH is

greater the the value of the SIZE attribute, the field

should scroll appropriately. The default number of

characters is unlimited.

SIZE

specifies the amount of display space allocated to this

input field according to its type. The default depends

on the user agent.

VALUE

The initial value of the field.

For example:

<p>Street Address: <input name=street><br>

Postal City code: <input name=city size=16 maxlength=16><br>

Zip Code: <input name=zip size=10 maxlength=10 value="99999-9999"><br>

8.1.2.2. Password Field: INPUT TYPE=PASSWORD

An <INPUT> element with `TYPE=PASSWORD' is a text field as above,

except that the value is obscured as it is entered. (see also: 10,

"Security Considerations").

For example:

<p>Name: <input name=login> Password: <input type=password name=passwd>

8.1.2.3. Check Box: INPUT TYPE=CHECKBOX

An <INPUT> element with `TYPE=CHECKBOX' represents a boolean choice.

A set of such elements with the same name represents an n-of-many

choice field. Required attributes are:

NAME

symbolic name for the form field corresponding to this

element or group of elements.

VALUE

The portion of the value of the field contributed by

this element.

Optional attributes are:

CHECKED

indicates that the initial state is on.

For example:

<p>What flavors do you like?

<input type=checkbox name=flavor value=vanilla>Vanilla<br>

<input type=checkbox name=flavor value=strawberry>Strawberry<br>

<input type=checkbox name=flavor value=chocolate checked>Chocolate<br>

8.1.2.4. Radio Button: INPUT TYPE=RADIO

An <INPUT> element with `TYPE=RADIO' represents a boolean choice. A

set of such elements with the same name represents a 1-of-many choice

field. The NAME and VALUE attributes are required as for check boxes.

Optional attributes are:

CHECKED

indicates that the initial state is on.

At all times, exactly one of the radio buttons in a set is checked.

If none of the <INPUT> elements of a set of radio buttons specifies

`CHECKED', then the user agent must check the first radio button of

the set initially.

For example:

<p>Which is your favorite?

<input type=radio name=flavor value=vanilla>Vanilla<br>

<input type=radio name=flavor value=strawberry>Strawberry<br>

<input type=radio name=flavor value=chocolate>Chocolate<br>

8.1.2.5. Image Pixel: INPUT TYPE=IMAGE

An <INPUT> element with `TYPE=IMAGE' specifies an image resource to

display, and allows input of two form fields: the x and y coordinate

of a pixel chosen from the image. The names of the fields are the

name of the field with `.x' and `.y' appended. `TYPE=IMAGE' implies

`TYPE=SUBMIT' processing; that is, when a pixel is chosen, the form

as a whole is submitted.

The NAME attribute is required as for other input fields. The SRC

attribute is required and the ALIGN is optional as for the <IMG>

element (see 5.10, "Image: IMG").

For example:

<p>Choose a point on the map:

8.1.2.6. Hidden Field: INPUT TYPE=HIDDEN

An <INPUT> element with `TYPE=HIDDEN' represents a hidden field.The

user does not interact with this field; instead, the VALUE attribute

specifies the value of the field. The NAME and VALUE attributes are

required.

For example:

8.1.2.7. Submit Button: INPUT TYPE=SUBMIT

An <INPUT> element with `TYPE=SUBMIT' represents an input option,

typically a button, that instructs the user agent to submit the form.

Optional attributes are:

NAME

indicates that this element contributes a form field

whose value is given by the VALUE attribute. If the NAME

attribute is not present, this element does not

contribute a form field.

VALUE

indicates a label for the input (button).

You may submit this request internally:

or to the external world:

8.1.2.8. Reset Button: INPUT TYPE=RESET

An <INPUT> element with `TYPE=RESET' represents an input option,

typically a button, that instructs the user agent to reset the form's

fields to their initial states. The VALUE attribute, if present,

indicates a label for the input (button).

When you are finished, you may submit this request:

You may clear the form and start over at any time: <input type=reset>

8.1.3. Selection: SELECT

The <SELECT> element constrains the form field to an enumerated list

of values. The values are given in <OPTION> elements. Attributes

are:

MULTIPLE

indicates that more than one option may be included in

the value.

NAME

specifies the name of the form field.

SIZE

specifies the number of visible items. Select fields of

size one are typically pop-down menus, whereas select

fields with size greater than one are typically lists.

For example:

<OPTION>Vanilla

<OPTION>Strawberry

<OPTION value="RumRasin">Rum and Raisin

<OPTION selected>Peach and Orange

</SELECT>

The initial state has the first option selected, unless a SELECTED

attribute is present on any of the <OPTION> elements.

8.1.3.1. Option: OPTION

The Option element can only occur within a Select element. It

represents one choice, and has the following attributes:

SELECTED

Indicates that this option is initially selected.

VALUE

indicates the value to be returned if this option is

chosen. The field value defaults to the content of the

<OPTION> element.

The content of the <OPTION> element is presented to the user to

represent the option. It is used as a returned value if the VALUE

attribute is not present.

8.1.4. Text Area: TEXTAREA

The <TEXTAREA> element represents a multi-line text field.

Attributes are:

COLS

the number of visible columns to display for the text

area, in characters.

NAME

Specifies the name of the form field.

ROWS

The number of visible rows to display for the text area,

in characters.

For example:

HaL Computer Systems

1315 Dell Avenue

Campbell, California 95008

</TEXTAREA>

The content of the <TEXTAREA> element is the field's initial value.

Typically, the ROWS and COLS attributes determine the visible

dimension of the field in characters. The field is typically rendered

in a fixed-width font. HTML user agents should allow text to extend

beyond these limits by scrolling as needed.

8.2. Form Submission

An HTML user agent begins processing a form by presenting the

document with the fields in their initial state. The user is allowed

to modify the fields, constrained by the field type etc. When the

user indicates that the form should be submitted (using a submit

button or image input), the form data set is processed according to

its method, action URI and enctype.

When there is only one single-line text input field in a form, the

user agent should accept Enter in that field as a request to submit

the form.

8.2.1. The form-urlencoded Media Type

The default encoding for all forms is `application/x-www-form-

urlencoded'. A form data set is represented in this media type as

follows:

1. The form field names and values are escaped: space

characters are replaced by `+', and then reserved characters

are escaped as per [URL]; that is, non-alphanumeric

characters are replaced by `%HH', a percent sign and two

hexadecimal digits representing the ASCII code of the

character. Line breaks, as in multi-line text field values,

are represented as CR LF pairs, i.e. `%0D%0A'.

2. The fields are listed in the order they appear in the

document with the name separated from the value by `=' and

the pairs separated from each other by `&'. Fields with null

values may be omitted. In particular, unselected radio

buttons and checkboxes should not appear in the encoded

data, but hidden fields with VALUE attributes present

should.

NOTE - The URI from a query form submission can be

used in a normal anchor style hyperlink.

Unfortunately, the use of the `&' character to

separate form fields interacts with its use in SGML

attribute values as an entity reference delimiter.

For example, the URI `http://host/?x=1&y=2' must be

written `<a href="http://host/?x=1&y=2"' or `<a

href="http://host/?x=1&y=2">'.

HTTP server implementors, and in particular, CGI

implementors are encouraged to support the use of

`;' in place of `&' to save users the trouble of

escaping `&' characters this way.

8.2.2. Query Forms: METHOD=GET

If the processing of a form is idempotent (i.e. it has no lasting

observable effect on the state of the world), then the form method

should be `GET'. Many database searches have no visible side-effects

and make ideal applications of query forms.

To process a form whose action URL is an HTTP URL and whose method is

`GET', the user agent starts with the action URI and appends a `?'

and the form data set, in `application/x-www-form-urlencoded' format

as above. The user agent then traverses the link to this URI just as

if it were an anchor (see 7.2, "Activation of Hyperlinks").

NOTE - The URL encoding may result in very long URIs, which cause

some historical HTTP server implementations to exhibit defective

behavior. As a result, some HTML forms are written using

`METHOD=POST' even though the form submission has no side-effects.

8.2.3. Forms with Side-Effects: METHOD=POST

If the service associated with the processing of a form has side

effects (for example, modification of a database or subscription to a

service), the method should be `POST'.

To process a form whose action URL is an HTTP URL and whose method is

`POST', the user agent conducts an HTTP POST transaction using the

action URI, and a message body of type `application/x-www-form-

urlencoded' format as above. The user agent should display the

response from the HTTP POST interaction just as it would display the

response from an HTTP GET above.

8.2.4. Example Form Submission: Questionnaire Form

Consider the following document:

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">

<title>Sample of HTML Form Submission</title>

<H1>Sample Questionnaire</H1>

<P>Please fill out this questionnaire:

<P>Female <INPUT NAME="gender" TYPE=RADIO VALUE="female">

<P>Number in family: <INPUT NAME="family" TYPE=text>

<P>Cities in which you maintain a residence:

<UL>

<LI>Miami <INPUT NAME="city" TYPE=checkbox VALUE="miami">

<LI>Other <TEXTAREA NAME="other" cols=48 rows=4></textarea>

</UL>

Nickname: <INPUT NAME="nickname" SIZE="42">

<P>Thank you for responding to this questionnaire.

</FORM>

The initial state of the form data set is:

name

gender

"male"

family

other

nickname

Note that the radio input has an initial value, while the

checkbox has none.

The user might edit the fields and request that the form be

submitted. At that point, suppose the values are:

name

"John Doe"

gender

"male"

family

"5"

city

"kent"

city

"miami"

other

"abc\ndefk"

nickname

"J&D"

The user agent then conducts an HTTP POST transaction using the URI

`http://www.w3.org/sample'. The message body would be (ignore the

line break):

name=John+Doe&gender=male&family=5&city=kent&city=miami&

other=abc%0D%0Adef&nickname=J%26D

9. HTML Public Text

9.1. HTML DTD

This is the Document Type Definition for the HyperText Markup

Language, level 2.

<!-- html.dtd

Document Type Definition for the HyperText Markup Language

(HTML DTD)

$Id: html.dtd,v 1.30 1995/09/21 23:30:19 connolly Exp $

Author: Daniel W. Connolly <connolly@w3.org>