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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]]>
Text ... is preferred to