A Dictionary of HTML META Tags

META tags have two possible attributes:

<META HTTP-EQUIV="name" CONTENT="content">
<META NAME="name" CONTENT="content">

META tags should be placed in the head of the HTML document, between the <HEAD> and </HEAD> tags (especially important in documents using FRAMES).

HTTP-EQUIV tags

META tags with an HTTP-EQUIV attribute are equivalent to HTTP headers. Typically, they control the action of browsers, and may be used to refine the information provided by the actual headers. Tags using this form should have an equivalent effect when specified as an HTTP header, and in some servers may be translated to actual HTTP headers automatically or by a pre-processing tool.

Note: While HTTP-EQUIV META tag appears to work properly with Netscape Navigator, other browsers may ignore them, and they are ignored by Web proxies, which are becoming more widespread. Use of the equivalent HTTP header, as supported by e.g. Apache server, is more reliable and is recommended wherever possible.

HTTP headers are defined in RFC1945 (HTTP/1.0) and RFC2068 (HTTP/1.1). Note that RFC2068 states that multiple headers with the same name may be present only if the values may be concatenated.

HTTP headers may be generated by CGI scripts, and in Apache and CERN httpd by using a side file containing metadata. Other servers may have other mechanisms to generate headers. Note that certain server-generated headers may not be overridden (such as Date), and that others are only meaningful with a non-200 status code. Using an HTTP header is preferable to using META tags, since the header will be understood by cache agents and proxies in addition to browsers, and metadata (such as PICS data) may be associated with image files, sound files, etc.

However, new HTTP headers should not be created without checking for conflict with existing ones since it is possible to interfere with server and proxy operation.

Content-Disposition

Source: RFC2183 - Specify application handler (Microsoft), e.g.

Content-Type: text/comma-separated-values
Content-Disposition: inline; filename=openinexcel.csv

Expires

Source: HTTP/1.1 (RFC2068)

The date and time after which the document should be considered expired. Controls cacheing in HTTP/1.0. In Netscape Navigator, a request for a document whose expires time has passed will generate a new network request (possibly with If-Modified-Since). An illegal Expires date, e.g. "0", is interpreted as "now". Setting Expires to 0 may thus be used to force a modification check at each visit.

Web robots may delete expired documents from a search engine, or schedule a revisit.

Dates must be given in RFC850 format, in GMT. E.g. (META tag):

<META HTTP-EQUIV="expires" CONTENT="Wed, 26 Feb 1997 08:21:57 GMT">

or (HTTP header):

Expires: Wed, 26 Feb 1997 08:21:57 GMT

In HTTP 1.0, an invalid value (such as "0") may be used to mean "immediately".

Note: While the Expires HTML META tag appears to work properly with Netscape Navigator, other browsers may ignore it, and it is ignored by Web proxies. Use of the equivalent HTTP header, as supported by e.g. Apache, is more reliable.

See also CacheNow for discussion about cache control, page expiry, etc.

Pragma

Controls cacheing in HTTP/1.0. Value must be "no-cache". Issued by browsers during a Reload request, and in a document prevents Netscape Navigator cacheing a page locally.

Content-Type

Source: HTTP/1.0 (RFC1945)

The HTTP content type may be extended to give the character set. As an HTTP/1.0 header, this unfortunately breaks older browsers. As a META tag, it causes Netscape Navigator to load the appropriate charset before displaying the page. E.g.

<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-2022-JP">

It is now recommended to always use this tag, even with the previously-default charset ISO-8859-1. Failure to do so may cause display problems where, for instance, the document uses UTF-8 punctuation characters but is displayed in ISO or ASCII charsets.

Content-Script-Type

E.g.

<META HTTP-EQUIV="Content-Script-Type" CONTENT="text/javascript">

Source: HTML 4.0

Specifies the default scripting language in a document. See MIMETYPES for applicable values.

Content-Style-Type

E.g.

<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">

Source: HTML 4.0

Specifies the default style sheet language for a document.

Default-Style

Source: HTML 4.0

Set the document's preferred style sheet, taken from an stylesheet specified elsewehere e.g. in a LINK element.

Content-Language

Source: HTTP/1.0, RFC1766

May be used to declare the natural language of the document. May be used by robots to categorize by language. The corresponding Accept-Language header (sent by a browser) causes a server to select an appropriate natural language document. E.g.

<META HTTP-EQUIV="Content-Language" CONTENT="en-GB">

or (HTTP header)

Content-language: en-GB

languages are specified as the pair (language-dialect); here, English-British

Refresh

Source: Netscape

Specifies a delay in seconds before the browser automatically reloads the document. Optionally, specifies an alternative URL to load. E.g.

<META HTTP-EQUIV="Refresh" CONTENT="3;URL=http://www.some.org/some.html">

or (HTTP header)

Refresh: 3;URL=http://www.some.org/some.html

In Netscape Navigator, has the same effect as clicking "Reload"; i.e. issues an HTTP GET with Pragma: no-cache (and If-Modified-Since header if a cached copy exists).

Note: If a script is executed which reloads the current document, the action of the Refresh tag may be undefined. (e.g. <body onLoad= "document.location='otherdoc.doc'>)

Window-target

Source: Jahn Rentmeister

Specifies the named window of the current page; can be used to stop a page appearing in a frame with many (not all) browsers. E.g.

<META HTTP-EQUIV="Window-target" CONTENT="_top">

or (HTTP header)

Window-target: _top

Ext-cache

Source: Netscape

Defines the name of an alternate cache to Netscape Navigator. E.g.

<META HTTP-EQUIV="Ext-cache" 
CONTENT="name=/some/path/index.db; instructions=User Instructions">

Set-Cookie

Source: Netscape Navigator

Sets a "cookie" in Netscape Navigator. Values with an expiry date are considered "permanent" and will be saved to disk on exit. E.g.

<META HTTP-EQUIV="Set-Cookie" 
CONTENT="cookievalue=xxx;expires=Friday, 31-Dec-99 23:59:59 GMT; path=/">

PICS-Label

Source: PICS

Platform-Independant Content rating Scheme. Typically used to declare a document's rating in terms of adult content (sex, violence, etc.) although the scheme is very flexible and may be used for other purposes.

Cache-Control

Source: HTTP/1.1

Specifies the action of cache agents. Possible values:

Public - may be cached in public shared caches
Private - may only be cached in private cache
no-cache - may not be cached
no-store - may be cached but not archived

Note that browser action is undefined using these headers as META tags.

Vary

Source: HTTP/1.1

Specifies that alternates are available. E.g.

<META HTTP-EQUIV="Vary" CONTENT="Content-language">

or (HTTP header)

Vary: Content-language

implies that if a header Accept-Language is sent an alternate form may be selected.

Lotus

The Lotus publishing tool generates Bulletin-Date and Bulletin-Text attributes. Bulletin-Text contains a document description.

NAME attributes

META tags with a name attribute are used for other types which do not correspond to HTTP headers. Sometimes the distinction is blurred; some agents may interpret tags such as "keywords" declared as either "name" or as "http-equiv".

Robots

Source: Spidering

Controls Web robots on a per-page basis. E.g.

<META NAME="ROBOTS" CONTENT="NOINDEX,FOLLOW">

Robots may traverse this page but not index it.

Altavista supports:

NOINDEX prevents anything on the page from being indexed.
NOFOLLOW prevents the crawler from following the links on the page and indexing the linked pages.
NOIMAGEINDEX prevents the images on the page from being indexed but the text on the page can still be indexed.
NOIMAGECLICK prevents the use of links directly to the images, instead there will only be a link to the page.

Google supports a NOARCHIVE extension to this scheme to request the Google search engine from caching pages; see the Google FAQ
See also the /robots.txtexclusion method.

Description

Source: Spidering, AltaVista, Infoseek.

A short, plain language description of the document. Used by search engines to describe your document. Particularly important if your document has very little text, is a frameset, or has extensive scripts at the top. E.g.

<META NAME="description" CONTENT="Citrus fruit wholesaler.">

Keywords

Source: AltaVista, Infoseek.

Keywords used by search engines to index your document in addition to words from the title and document body. Typically used for synonyms and alternates of title words. E.g.

<META NAME="keywords" CONTENT="oranges, lemons, limes">

Author

Source: Publishing tools, e.g. Netscape Gold

Typically the unqualified author's name.

Generator

Source: Publishing tools, e.g. Netscape Gold, FrontPage, etc.

Typically the name and version number of a publishing tool used to create the page. Could be used by tool vendors to assess market penetration.

Formatter

Source: Publishing tools - Microsoft FrontPage

Classification

Source: Netscape Gold

Undefined.

Copyright

Source: Publishing tools

Typically an unqualified copyright statement.

Rating

Source: mk-metas, Weburbia (safe for kids)

Simple content rating.

VW96.ObjectType

Source: mk-metas

Based on an early version of the Dublin Core report, using a defined schema of document types such as FAQ, HOWTO.

Defined by Queen's University of Belfast; a restricted set including e.g. "Contact Information", "Image".

Dublin Core

DC.TITLE, DC.CREATOR, DC.SUBJECT , DC.DESCRIPTION , DC.PUBLISHER , DC.CONTRIBUTORS , DC.DATE , DC.TYPE, DC.FORMAT , DC.IDENTIFIER, DC.SOURCE , DC.LANGUAGE , DC.RELATION, DC.COVERAGE, DC.RIGHTS

Dublin Core Elements. See the Reference Description

HTML 4.0

The HTML 4.0 Specification is now available.

HTdig

htdig-keywords, htdig-noindex

HTdig tags. See the HTdig META page.

DC-CHEM

DC-CHEM. Chemical Metadata extensions

HTdig notification

htdig-email, htdig-notification-date, htdig-email-subject - see HTdig notification.

searchBC

searchBC is a regional search engine which uses a number of common tags such as Keywords. revisit is used as a hint for scheduling revisits.

Page-Enter, Page-Exit, Site-Enter, Site-Exit

Source: Microsoft DHTML (Filters & Transitions)

Defines special effects transition; e.g.

<meta http-equiv="Page-Enter"
content="revealTrans(Duration=3.0,Transition=2)">

See e.g. Transitions Between Pages (Ruleweb)

contributor
custodian
custodian_contact
custodian_contact_position
east_bounding_coordinate
north_bounding_coordinate
relation
reply-to
south_bounding_coordinate
west_bounding_coordinate

Other Organisations

DMV MetaData for Mathematical Papers
Maple Square (ex. Sympatico)

Agent Markup Language

See the AML pages.

Agent markup Language Version

GeoCities

See GeoCities categorize.

GILS

Government Information Locator Service - a US government initiative. See

Washington GILS metadata attribute set
GILS profile (version 2)

IMS

See the IMS Project homepage.

Dictionary

Fireball

The German search engine Fireball. See the metadata page and meta-tag generator. Supports Author, Publisher, Keywords, Description plus page-topic, page-type.

Geotags

Geographic Tagging for Resource Discovery.

Geo.Region - Geographic regions from ISO3166-2
Geo.Placename - Free Text place name
Geo.Position - Latitude;Longitude in decimal degrees using the WGS84 datum.

Google

googlebot: noarchive - do not allow google to display cached content
googlebot: nosnippet - do not allow google to display excerpt or cached content
googlebot: noindex - similar to the robots meta element
googlebot: nofollow

See Google Remove Content

MSSmartTags

MSSmartTagsPreventParsing: TRUE - prevent Microsoft Smart Tags being applied to a page

See glassdog.com/smarttags, office.microsoft.com. However, it looks at the moment as if SmartTags have been abandoned.

UnSpam

An initative of unspam.com to forbid compliant robots from harvesting email addresses. Usage:

<meta name="no-email-collection" value="[link to your terms]" />

Replace the [link to your terms] with a link to your terms of use page. Alternatively you may include a link to www.unspam.com/noemailcollection
See how_to_avoid_spambots

Miscellaneous

Version
Template
Operator
Creation
Host
Document
Subject
Build
Distribution - global,local, iu
Resource-type - document (for ALIWeb)
Location (geographic location; from Sympatico)

Deprecated:

Random Text (e.g., META NAME="Tom Jones")

Web Counts

Attributes in use counted by a Web robot here.
Also counted 3 July 97.
IAFA Template Statistics from the ROADS project

Other Resources

Resource Description Framework (RDF) - a W3C specification
The META Generator (CGI script)
REL, REV tags
Resource Description (Connolly)
Metadata Architecture (TimBL, Jan 97)
META reference by Galactus
HTML 3.2
META Tagging for Search Engines at stars.com
aditudes metatags - links, some info on search engine support
draft-musella-html-metatag-01.txt, version 2
HTML Writers Guild FAQ
Jaggery the Rascal's notes.
metadata at ERIN
report from the May 96 Indexing Workshop
draft-daviel-metadata-reg.txt (not.)
Dublin Core Generator at UKOLN
Dublin Core Metadata Template at Nordic Metadata Project
Linking Metadata ( draft-daviel-metadata-link-00.txt)
ADAM Quick Guide to Metadata

Thesauri

GETTY Art & Architecture Thesaurus
GETTY Artist Names Thesaurus
TGN - GETTY Thesaurus of Geographic Names
TGM I US Library of Congress Thesaurus for Graphic Materials I: Subject Terms
TGM II US Library of Congress Thesaurus for Graphic Materials II: Genre and Physical Characteristic Terms
LIV US Library of Congress Legislative Indexing Vocabulary
GLIN US Library of Congress Global Legal Information Network (GLIN) Thesaurus
ISSN (International Standard Serials Number)
LCSH (paper/CDROM)
LCSH, (telnet)