rfc1866.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   Some elements only have a start-tag without an end-tag. For example,
   to create a line break, use the `<BR>' tag.  Additionally, the end
   tags of some other elements, such as Paragraph (`</P>'), List Item
   (`</LI>'), Definition Term (`</DT>'), and Definition Description
   (`</DD>') elements, may be omitted.

   The content of an element is a sequence of data character strings and
   nested elements. Some elements, such as anchors, cannot be nested.
   Anchors and character highlighting may be put inside other
   constructs. See the HTML DTD, 9.1, "HTML DTD" for full details.

      NOTE - The SGML declaration for HTML specifies SHORTTAG YES, which
      means that there are other valid syntaxes for tags, such as NET
      tags, `<EM/.../'; empty start tags, `<>'; and empty end-tags,
      `</>'. Until support for these idioms is widely deployed, their
      use is strongly discouraged.

3.2.3. Names

   A name consists of a letter followed by letters, digits, periods, or
   hyphens. The length of a name is limited to 72 characters by the
   `NAMELEN' parameter in the SGML declaration for HTML, 9.5, "SGML
   Declaration for HTML". Element and attribute names are not case
   sensitive, but entity names are.  For example, `<BLOCKQUOTE>',
   `<BlockQuote>', and `<blockquote>' are equivalent, whereas `&amp;' is
   different from `&AMP;'.

   In a start-tag, the element name must immediately follow the tag open
   delimiter `<'.







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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&#62;b">' or `<IMG
            SRC="eq1.jpg" alt="a&gt;b">'.

        * A name token (a sequence of letters, digits, periods, or
        hyphens). Name tokens are not case sensitive.

            NOTE - Some historical implementations allow any
            character except space or `>' in a name token.

   In this example, <img> is the element name, src is the attribute
   name, and `http://host/dir/file.gif' is the attribute value:

   <img src='http://host/dir/file.gif'>

   A useful technique for computing an attribute value literal for a
   given string is to replace each quote and white space character by an
   entity reference or numeric character reference as follows:

                     ENTITY      NUMERIC
           CHARACTER REFERENCE   CHAR REF     CHARACTER DESCRIPTION
           --------- ----------  -----------  ---------------------
             HT                  &#9;         Tab
             LF                  &#10;        Line Feed
             CR                  &#13;        Carriage Return
             SP                  &#32;        Space
             "       &quot;      &#34;        Quotation mark
             &       &amp;       &#38;        Ampersand




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   For example:

   <IMG SRC="image.jpg" alt="First &quot;real&quot; example">

   The `NAMELEN' parameter in the SGML declaration (9.5, "SGML
   Declaration for HTML") limits the length of an attribute value to
   1024 characters.

   Attributes such as ISMAP and COMPACT may be written using a minimized
   syntax (see 7.9.1.2 "Omitted Attribute Name" in [SGML]). The markup:

   <UL COMPACT="compact">

   can be written using a minimized syntax:

   <UL COMPACT>

   NOTE - Some historical implementations only understand the minimized
   syntax.

3.2.5. Comments

   To include comments in an HTML document, use a comment declaration. A
   comment declaration consists of `<!' followed by zero or more
   comments followed by `>'. Each comment starts with `--' and includes
   all text up to and including the next occurrence of `--'. In a
   comment declaration, white space is allowed after each comment, but
   not before the first comment.  The entire comment declaration is
   ignored.

      NOTE - Some historical HTML implementations incorrectly consider
      any `>' character to be the termination of a comment.

   For example:

    <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
    <HEAD>
    <TITLE>HTML Comment Example</TITLE>
    <!-- Id: html-sgml.sgm,v 1.5 1995/05/26 21:29:50 connolly Exp  -->
    <!-- another -- -- comment -->
    <!>
    </HEAD>
    <BODY>
    <p> <!- not a comment, just regular old data characters ->







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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.

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

   This document type declaration refers to the HTML DTD in 9.1, "HTML
   DTD".

      NOTE - If the body of a `text/html' message entity does not begin
      with a document type declaration, an HTML user agent should infer
      the above document type declaration.

   <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Level 2//EN">

   This document type declaration also refers to the HTML DTD which
   appears in 9.1, "HTML DTD".

   <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Level 1//EN">

   This document type declaration refers to the level 1 HTML DTD in 9.3,
   "Level 1 HTML DTD". Form elements must not occur in level 1
   documents.

   <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Strict//EN">
   <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Strict Level 1//EN">

   These two document type declarations refer to the HTML DTD in 9.2,
   "Strict HTML DTD" and 9.4, "Strict Level 1 HTML DTD". They refer to
   the more structurally rigid definition of HTML.

   HTML user agents may support other document types. In particular,
   they may support other formal public identifiers, or other document
   types altogether. They may support an internal declaration subset
   with supplemental entity, element, and other markup declarations.

3.4. Example HTML Document

    <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
    <HTML>
    <!-- Here's a good place to put a comment. -->
    <HEAD>
    <TITLE>Structural Example</TITLE>
    </HEAD><BODY>
    <H1>First Header</H1>
    <P>This is a paragraph in the example HTML file. Keep in mind



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    that the title does not appear in the document text, but that
    the header (defined by H1) does.</P>
    <OL>
    <LI>First item in an ordered list.
    <LI>Second item in an ordered list.
      <UL COMPACT>
      <LI> Note that lists can be nested;
      <LI> Whitespace may be used to assist in reading the
           HTML source.
      </UL>
    <LI>Third item in an ordered list.
    </OL>
    <P>This is an additional paragraph. Technically, end tags are
    not required for paragraphs, although they are allowed. You can
    include character highlighting in a paragraph. <EM>This sentence
    of the paragraph is emphasized.</EM> Note that the &lt;/P&gt;
    end tag has been omitted.
    <P>
    <IMG SRC ="triangle.xbm" alt="Warning: ">
    Be sure to read these <b>bold instructions</b>.
    </BODY></HTML>

4. HTML as an Internet Media Type

   An HTML user agent allows users to interact with resources which have
   HTML representations. At a minimum, it must allow users to examine
   and navigate the content of HTML level 1 documents. HTML user agents
   should be able to preserve all formatting distinctions represented in
   an HTML document, and be able to simultaneously present resources
   referred to by IMG elements (they may ignore some formatting
   distinctions or IMG resources at the request of the user). Level 2
   HTML user agents should support form entry and submission.

4.1. text/html media type

   This specification defines the Internet Media Type [IMEDIA] (formerly
   referred to as the Content Type [MIME]) called `text/html'. The
   following is to be registered with [IANA].

    Media Type name
            text

    Media subtype name
            html

    Required parameters
            none




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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 <FORM>
            element. Level 2 includes form processing. Level 2 is
            the default.

    Charset
            The charset parameter (as defined in section 7.1.1 of
            RFC 1521[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



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   other hand, references to undeclared entities should be treated as
   data characters.

   For example:

    <div class=chapter><h1>foo</h1><p>...</div>
      => <H1>,"foo",</H1>,<P>,"..."
    xxx <P ID=z23> yyy
      => "xxx ",<P>," yyy
    Let &alpha; &amp; &beta; be finite sets.
      => "Let &alpha; & &beta; be finite sets."

   Support for notifying the user of such errors is encouraged.

   Information providers are warned that this convention is not binding:
   unspecified behavior may result, as such markup does not conform to
   this specification.

4.2.2. Conventional Representation of Newlines

   SGML specifies that a text entity is a sequence of records, each
   beginning with a record start character and ending with a record end
   character (code positions 10 and 13 respectively) (section 7.6.1,
   "Record Boundaries" in [SGML]).

   [MIME] specifies that a body of type `text/*' is a sequence of lines,
   each terminated by CRLF, that is, octets 13, 10.

   In practice, HTML documents are frequently represented and
   transmitted using an end of line convention that depends on the
   conventions of the source of the document; frequently, that
   representation consists of CR only, LF only, or a CR LF sequence.
   Hence the decoding of the octets will often result in a text entity
   with some missing record start and record end characters.

   Since there is no ambiguity, HTML user agents are encouraged to infer
   the missing record start and end characters.

   An HTML user agent should treat end of line in any of its variations
   as a word space in all contexts except preformatted text. Within
   preformatted text, an HTML user agent should treat any of the three
   common representations of end-of-line as starting a new line.

5. Document Structure

   An HTML document is a tree of elements, including a head and body,
   headings, paragraphs, lists, etc. Form elements are discussed in 8,
   "Forms".



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