INTERNET DRAFT Davide Musella
draft-musella-html-metatag-02.txt National Research Council
January 29, 1996
Expires in six months
The META Tag of HTML
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as ``work in progress.''
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Cost) or
ftp.isi.edu (US West Coast).
Distribution of this document is unlimited. Please send comments to
Davide Musella, davidmsl@anti.tesi.dsi.unimi.it or to
davide@jargo.itim.mi.cnr.it , (voice) +39.(0)2.70643271
Abstract
This document defines a strict synopsis for the META Tag of HTML.
The grammar is extended to the contents of the HTTP-EQUIV field,
defining a set of words to use to allow document cataloguing.
1. Introduction
Now the synopsis of the META HTTP-EQUIV Tag is not severe, allowing so
the use of different key words to define the same things.
The functions like this:
or:
could reppresent the same concepts with two different syntax.
The aim of this Draft is to define which are the words to use to
define the contents of an HTML document.
There are, also, some easy rules to implement a binary logic (AND or
OR) for the CONTENT field.
2. The META Tag
The META element is used within the HEAD element to embed documents
meta-information not defined by other HTML elements. Such information
can be extracted by servers/clients for use in identifying, indexing
and cataloging specialized document meta-information.
Although it is generally preferable to used named elements that have
well defined semantics for each type of meta-information, such as
title, this element is provided for situations where strict SGML
parsing is necessary and the local DTD is not extensible.
In addition, HTTP servers can read the contents of the document head
to generate response headers corresponding to any elements defining
a value for the attribute HTTP-EQUIV. This provides document authors
with a mechanism (not necessarily the preferred one) for identifying
information that should be included in the response headers of an
HTTP request.
The META element has three attributes:
- HTTP-EQUIV
- NAME
- CONTENT
The HTTP-EQUIV and the NAME attributes are mutually exclusives.
3. HTTP-EQUIV.
This attribute binds the element to an HTTP response header. If the
semantics of the HTTP response header named by this attribute is
known, then the contents can be processed based on a well defined
syntactic mapping, whether or not the DTD includes anything about it.
HTTP header names are case insensitive. If absent, the NAME
attribute should be used to identify the meta-information and it
should not be used within an HTTP response header.
It is possible to use any text string, but if you want to define
these properties you have to use the following words:
keywords: to indicate the keywords of the document
author: to indicate the author of the document
timestamp: to indicate when the document is authored
(HTTP-date format)
expire: to indicate the expire date of the document
(HTTP-date format)
language: to indicate the language of the document
(using ISO3316 code or ISO639 code)
abstract: to indicate the abstract of the document
organization: to indicate the organization of the author
revision: to indicate the revision number of the document
(format: 00, 01, 02, or 000, 001, ...)
An HTTP server must process these tags for an HEAD HTTP requestr.
Do not name an HTTP-EQUIV attribute the same as a response header
that should typically only be generated by the HTTP server. Some
inappropriate names are "Server", "Date", and "Last-Modified".
Whether a name is inappropriate depends on the particular server
implementation. It is recommended that servers ignore any META
elements that specify HTTP equivalents (case insensitively) to their
own reserved response headers.
4. NAME.
This attributes can be used to define some properties such as "number
of pages" or "preferred browser" or any info an author want to insert
in his document. The keywords indicates in the previous paragraph for
the HTTP-EQUIV are still valid also in the NAME context.
An example:
or
Do not use the META element to define information that should be
associated with an existing HTML element.
5. CONTENT
Used to supply a value for a named property.
It can contain more than one single information; it is possible to
use the Boolean operator (AND, OR) to insert a Boolean definition of
the field.
The AND operator will be represented by the SPACE (ASCII[32]) and the
OR operator by the COMMA (ASCII[44]).
The AND operator is processed before the OR operator. So a string
like this: "Red ball, White pen" means :"(Red AND ball) OR (White AND pen)".
Example:
The spaces between a comma and a word or vice versa are ignored.
6. Cataloguing an HTML document
These 'keywords' were specifically conceived to catalogue HTML documents.
This allows the software agents to index at best your own document.
To do a preliminary indexing, it's important to use at least the
HTTP-EQUIV meta-tag "keywords".