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:
Parsing Example
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
| |
| \-
| |
| \-"Parsing Example"
| |
| \-
|
\-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 a element. The contains ,
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").
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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"
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 < def => "abc ","<"," def"
abc < 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
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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 `&'.
In a start-tag, the element name must immediately follow the tag open
delimiter `<'.
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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="eq1.jpg" alt="a>b">' should be
written `<IMG SRC="eq1.jpg" alt="a>b">' or `<IMG
SRC="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:
<img src='http://host/dir/file.gif'>
A useful technique for computing an attribute value literal for a
given string is to replace each quote and white space character by an
entity reference or numeric character reference as follows:
ENTITY NUMERIC
CHARACTER REFERENCE CHAR REF CHARACTER DESCRIPTION
--------- ---------- ----------- ---------------------
HT Tab
LF
Line Feed
CR
Carriage Return
SP Space
" " " Quotation mark
& & & Ampersand
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For example:
<IMG SRC="image.jpg" alt="First "real" example">
The `NAMELEN' parameter in the SGML declaration (9.5, "SGML
Declaration for HTML") limits the length of an attribute value to
1024 characters.
Attributes such as ISMAP and COMPACT may be written using a minimized
syntax (see 7.9.1.2 "Omitted Attribute Name" in [SGML]). The markup:
<UL COMPACT="compact">
can be written using a minimized syntax:
<UL COMPACT>
NOTE - Some historical implementations only understand the minimized
syntax.
3.2.5. Comments
To include comments in an HTML document, use a comment declaration. A
comment declaration consists of `<!' followed by zero or more
comments followed by `>'. Each comment starts with `--' and includes
all text up to and including the next occurrence of `--'. In a
comment declaration, white space is allowed after each comment, but
not before the first comment. The entire comment declaration is
ignored.
NOTE - Some historical HTML implementations incorrectly consider
any `>' character to be the termination of a comment.
For example:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HEAD>
<TITLE>HTML Comment Example
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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
Structural Example
First Header
This is a paragraph in the example HTML file. Keep in mind
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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.
Be sure to read these bold instructions.
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
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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
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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):
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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.
...
--
>
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]]>
%ISOlat1;
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]]>