INTERNET DRAFT Davide Musella
draft-musella-html-metatag-01.txt National Research Council
20 December 1995
The META Tag of HTML
Status of this Memo
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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 cataloging.
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:
<META HTTP-EQUIV = "Keywords" CONTENT = "Italy, Tourism">
or
<META HTTP-EQUIV = "Keys" CONTENT = "Italy, Tourism">
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 (HTML 3.0 definition)
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
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 not case sensitive. If absent, the NAME
attribute should be used to identify this 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
expire: to indicate the expire date of the document
language: to indicate the language of the document
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
public (Boolean): to indicate if the document is available to
everybody or not
An HTTP server must process these tags for an HEAD HTTP request,
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
author, publication date etc. If absent the name can be assumed to be
the same as the value of HTTP-EQUIV.
An example:
<META NAME= "Editor" CONTENT = "McDraw Bill">
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.
If it's used with the HTTP-EQUIV 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 ball" means :"ball AND (red OR white)".
Examples:
<META HTTP-EQUIV= "Keywords" CONTENT= "Italy Product, Italy Tourism">
The spaces between a comma and a word or vice versa are ignored.
6. Cataloging an HTML document
These 'keywords' were specifically conceived for exaustively and
completely catalogue the HTML document.
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".