The meta element allows authors to attach additional information (representing metadata) to their documents. This information can be used by the user agent for rendering content, it can provide meta information for indexing, it can be used to simulate http Response Headers, and it also can be used to reload the document. The additional information also represents various kinds of metadata that cannot be expressed using the title, base, link, style and script elements.
The meta element belongs in a document’s head and has no content; its attributes define name/value pairs associated with the document. The meta element information is machine-parsable (read: machine tags and all browsers expose meta information via the dom. These name/value pairs can be used by the server to further define the document type to the user agent.
The meta element is a void element: an element whose content model never allows it to have contents under any circumstances; It requires exactly one of the attributes of name, http-equiv and charset must be specified. If the name or http-equiv attributes are specified then the content attribute must also be specified, otherwise omit content.
html5, whatwg and the dcmi are all working to create a standard lists of meta properties, however currently none exists.
name="" Attribute
The name="" attribute is the name in the name/value pair and represents document-level metadata. This representation specifies what aspect of metadata is being set. If the content="" attribute is omitted then the value of the name/value pair is an empty string. If not provided, the name of the name/value pair is taken from the http-equiv="" attribute.
The name="" attribute must be a defined metadata name or a registered metadata name. name IDL attributes must reflect the respective content="" attributes of the same name.
w3c Defined Metadata Names
application-name: the value of the content="" attribute must be a string representing the name of the Web App the page represents. If document is not a Web App, don’t use it. Cannot have more than one per document. User Agents can use application name in ui instead of the title element because title could have status messages, etc. relevant to the status of the page at a particular time.
author: value of the content="" attribute must be a string giving the name of the author(s) of the document.
description: value of content="" attribute must be a string describing the page. Must be appropriate for use in a search engine. Document cannot have more than one.
generator: value of the content="" attribute must be a string identifying software used to generate the document. Do not use this value on hand-authored pages (notepad denied!).
keywords: value of content="" attribute must be a set of comma-separated strings, where each string is a relevant keyword to the document.
w3c Other Defined Metadata Names
keyword: actual name being defined; should not be similar to any other defined name (like differing only in case).
brief description: short, non-normative description of what the metadata name’s meaning is, including the format the value is required to be in.
specification: link to a more detailed description of metadata name’s semantics and requirements.
synonyms: list of names that have exactly the same processing requirements. do not use the named defined to be synonyms, they’re only intended to allow user agents to support legacy content. Synonms not in practice can be removed, only names that need to be processed as synonyms for compatibility with legacy content are to be registered this way.
status: has three possible values: proposed, ratified, and discontinued
name="status" content="proposed": name has not received wide peer review and approval; name has been proposed and is or soon will be in use.
name="status" content="ratified": name has received wide peer review and approval. its specification unambiguously defines how to handle pages using the name including when used incorrectly.
name="status" content="discontined": metadata name has received wide peer review and has been found wanting. May be in use on existing pages, but new pages should not used it. If anything, “brief description” and “specification” entries give details of what the author should use.
whatwg Registered Metadata Names (technically none so far)
baiduspider – synonym for robots targeting Baidu only.googlebot – synonym for robots targeting Googlebot only.ia_archive – synonym for robots targeting Archive and Alexa only.msnbot – synonym for robots targeting Bing only.robots – comma-separated list of operators telling search engine bots how to treat content.slurp – synonym for robots targeting Yahoo! only.teoma – synonym for robots targeting Teoma and Ask.com only.viewport – allows documents to specify size, zoom factor and orientation of the viewport used as the base for document’s initial containing block. The following properties can be used in the value of the content="" attribute: width, height, initial-scale, minimum-scale, maximum-scale, user-scalable.
audience – aids search engine classification and aids directory compiliations by providing the audience most appropriate for the page. Values are case-insensitive and comma-separated (singular and plural values are equal).bot- – represents all bots prefixed with bot-.created – document creation datetime (ISO8601 date); must follow w3c ISO-8601 datetime profile with a granularity of “complete date” or finer.creator – off-Web/pre-Web creator of a work for which an author authored a document, so the creator and author can be different people. One element represents one creator; multiple creators need to be represented by multiple creator elemetns.datetime-coverage – value is a non-vague date or non-vague time (not a range) expressing which time frame is most relevant to the content.datetime-coverage-end – identical to datetime-coverage except only representing the end. When used without datetime-coverage-start, it is interpreted as ending a range without a start.datetime-coverage-start – identical to datetime-coverage except representing only the start; if used without datetie-coverage-end, is interpreted as starting a range with no end.datetime-coverage-vague – identical to datetime-coverage except its value is not clear; use when datetime-coverage, datetime-coverage-end, datetime-coverage-start are all inappaproiate (example: Tuesdays).DC – stands for Dublin Core, maintained by the dcmi, reserves all strings that begin with DC..dir-content-pointer – helps search engines organize results by identifying similar sections of pages in a directory with a standard vocabulary. Useful when using different conventions for displaying or printing content. Recognized values are pointer types to which numbers may be suffixed: start, toc (table of contents), intro, abstract, main, bibliography, index, afterword, update, credit and author bio. Number suffixes tell the search engine/directory to arrange like itmes in numerical order within the results. Each directory and subdirectory has its own sequence.expires – defines expiration date of the document which can be used in preparation for an upcoming event (when you have a pre-set date when the document will no longer be valid, like a sign-up form for an event). Search engines should remove this page from their main search results after the expiration date or by telling the user the result is out of date.format-print – informs operating system/printer driver of the preferred print medium (like paper size). Recognized values are letter, A4, legal, A5, B5, monarch, envelope 10, envelope 6-3-4 as well as values with integers and decimals, like 8.5 x 11, paper (default color), weight (usually 20lb. stock). You can specify a medium of the given color or mixed by using white, yellow, pink, blue, green, violet or multicolor. Letterhead, p2 letterhead (letterhead for all pages minus first page), watermark and plain (not preprinted/not letterhead).geographic-coverage – specify geographic relevance of content.keywords-not – negative keywords that distinguish closely-related themes from a document’s theme. Supports Boolean not searches.page-datetime – tells search engines recency or relevance to an event date.
page-version – Versions regardless of date may show consecutiveness and can replace vague dates; a version number can be more useful in this case. Versions 0 and 0.n signify beta versions, where .n is number of places and 1 or higher implies final-release versions.
publisher – provides the document’s publisher, which often differs from creator/author when the publisher is an institution.referrer – controls the sharing of referrer information with linked resources and followed links at the meta level. The content attribute accepts three values, always, default (include referrer information in non-secure conext or for https resources with same origin) and never; The never value is redundant with link rel="nofollow" and supplants said link element, which provides more control.resolutions – specifies high-resolution versions of images that the browsers should use in place of lower-resolution default images if a high-resolution screen is detected to be in use.rights – used to assert intellectual property rights in source code.rights-standard – enable search engines to compile the types of rights allocated to the document; the example belows implies that the Page code is cc By Attribution, Share alike<meta name="rights-standard" content="code;cc:bysa" />subj-... – To classify by subject a page’s content, a standard subject taxonomy that will be recognized by a search engine or directory will help. Because many such high-quality taxonomies exist, only a prefix is proposed. Over time, particular taxonomies, in print or online, may be recognized here and keywords assigned for each.
MSSmartTagsPreventParsing – ie6 beta feature allowed browser to add information that wasn’t supplied by the document; this prevents that.
meta Pragma Directives
The http-equiv attribute is an enumerated attribute (taking one of a finite set of keywords), and if a meta http-equiv element is present within the document, the user agent must run the algorithim appropriate for that State. keywords and appropriate algorithims below:
State Content Language maps to keyword content-language; Content language state (http-equiv="content-language"): this pragma sets the pragma-set default language; until successfully processed, there is no pragma-set default language.
note: this will trigger a warning in validators, use lang attribute instead.
State Encoding Declaration maps to keyword content-type; Encoding declaration state (http-equiv="content-type") alternative form of setting charset="" attribute; is a character encoding declaration. Encoding declaration state’s user agent requirements are entirely handled by the parsing section of the specification.
State Default Style maps to keyword default-style; Default style state (http-equiv="default-style"): this pragma sets the name of the default alternative style sheet.
State Refresh maps to keyword refresh; Refresh state (http-equiv="refresh"): pragma acts as a timed redirect.
State Cookie Setter maps to keyword set-cookie although Cookie Setter is non-conforming; Cookie setter (http-equiv="set-cookie"): pragma sets http cookie. Is non-conforming, you should use real http Headers instead.
Pragma Directive http-equiv="" Attribute
The http-equiv="" attribute is the name in the name/value pair; tells the server to include said pair in the mime document header that is passed to the browser before actually sending the document. When the http-equiv="" attributee is used, the server adds these name/value pairs to the content header it sends to the browser.
The http-equiv="" attribute is restricted to these values: refresh, default-style and content-type in html5.
http-equiv="refresh" Pragma Directive
The http-equiv="" attribute whose value is refresh represents a pragma directive specifying either a number of seconds after which to reload the current page, or a number of seconds after which to reload a different page and the url for the replacement page.
http-equiv="default-style" (Preferred Stylesheet) Pragma Directive
meta http-equiv element attribute whose value is default-style represents a pragma directive that specifies the document’s preferred stylesheet. content=default-style-name where default-style-name is the name of the preferred stylesheet and must either match the value of the link title="name" that also has href="" attribute referencing the location of said stylesheet or, the names must match the value of the style title="name" whose contents are a css stylesheet.
http-equiv="content-language" (Default Language) Pragma Directive
meta http-equiv element attribute whose value is content-language represents a pragma directive specifying a document-wide default language; this is obselete, specify the language on the root element instead.
http-equiv="content-type" (Document Character-Encoding Declaration) Pragma Directive
meta http-equiv element attribute whose value is content-type and has an accompanying content attribute and value represents a character encoding declaration.
meta http-equiv="content-type" indicates the meta element is in the encoding declaration state and represents a character encoding declaration.
meta http-equiv="content-type" content="meta-charset string" is a specially formatted string providing a character encoding name whose value is content-type and which has an accompanying content attribute and value is said to be in the encoding declaration state.
Non-standard meta http-equiv Values
AllowContent-EncodingContent-LanguageContent-LengthContent-TypeDateExpiresLast ModifiedLocationSet-CookieWWW-Authenticate
content Attribute
The content attribute is the value in the name/value pair. The value can be any valid string and should always be used in conjunction with a name or http-equiv attribute. It gives value of the document metadata or pragma directive when the meta element is used for these purposes. The content contains the actual metadata defined by the The name attribute.
charset Attribute (Document Character-Encoding Declaration)
The charset attribute specifies the character encoding used by the document (aka character encoding declaration). It has no effect on xml documents, and is only used to facilitate migration to/from xhtml. The charset attribute represents a document’s character encoding declaration when an html document is serialized to string form. There must be no more than one meta element with charset attribute per document.
The charset attribute represents a character encoding declaration, where charset="name" specifies a character encoding name specified by the iana registry that has a Name or Alias field labeled as “preferred mime name“, or if none of the Alias fields are so labeled, a Name field in the registry.
scheme Attribute
The scheme attribute defines the scheme that should be used to interpret the property’s value, which should be defined within the profile specified by the profile attribute of the head element. It provides additional information about the meta information; used in conjunction with the profile attribute of the head element (which provides a pointer to instructions about the contents of the profile which are directly related to meta name attribute values). The value of scheme is a uri specifying the location of the profile information on the server.
The scheme attribute is obselete; use only one scheme per field or make the scheme declaration part of the value.
Bibliography
