Difference between revisions of "MetaExtensions"
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== Process ==
== Process ==
Revision as of 20:19, 25 April 2009
This page lists the allowed extension values for the name="" attribute of the <meta> element in HTML5. You may add your own values to this list, which makes them legal HTML5 metadata names. We ask that you try to avoid redundancy; if someone has already defined a name that does roughly what you want, please reuse it.
|Keyword||Brief description||Link to more details||Synonyms||Status|
|keywords-not||A comma-separated list of negative keywords that distinguish a closely-related theme from this page's true theme, to support Boolean NOT searches often more realistically than visible text can, especially when both themes share the same lexicon.||W3C Bug 6609||keywords-negative; keyword-negative; negative-keywords; negative-keyword; keywords-neg; keyword-neg; neg-keywords; neg-keyword; not-keywords; not-keyword; keyword-not||Proposal|
|robots||A comma-separated list of operators explaining how search engine crawlers should treat the content. Possible values are "noarchive" to prevent cached versions, "noindex" to prevent indexing, and "nofollow" works as the link rel value with the same name. This meta name is already supported by every popular search engine.||Robots exclusion protocol, Googlebot, Yahoo! Slurp, and Ask.com Teoma||Proposal|
|page-datetime||Better ranking in search engine results for recency or relevance to an event date would be aided by a standard format robots can parse. Users would save search time by not having to load many pages to find which ones are new or date-relevant. To supply a consistent and known format, the value for this keyword is a date-time expression formed in accordance with http://www.w3.org/TR/NOTE-datetime (albeit a note that's at W3C only for discussion). Any of the six levels of granularity are acceptable, such as expressing only a year. Should this keyword appear more than once within the head element, only the first one so appearing is determinative.||Proposal|
|page-version||Pages may be revised several times in a day. While date-time given to a granularity of a fraction of a second would often suffice, when a page has to be approved more than once before posting, any or no such time may be correct (without this keyword, a comment could be necessary but probably not parsable by an engine). In addition, versions regardless of date may show consecutiveness and can replace a date that must be vague. In that case, a version number may be more useful for searches and so a robot-parsable format is needed. The keyword's value is stated in ASCII digits, is any nonnegative base-10 rational number expressed as an integer or a decimal, and may be padded with any number of leading zeros to support extraction for ASCII sorting. Should this keyword appear more than once within the head element, only the first one so appearing is determinative.||Proposal|
|geographic-coverage||The author may be the best expert on the geographic relevance of the content. Leaving that to search engine analysis may be too chancy without search engine optimization, which analysis is difficult to apply by algorithm to, e.g., historical papers and epidemiological studies which may mention locales only once. Absence of the keyword defaults to a value of world (not universe), unless the search engine chooses to interpret the page or larger unit for some other value, probably based on other than just contact information given in the website. The value for this keyword is a semicolon-separated list of one or more place-values, the order of which do not matter. One place-value will use commas to separate, in order, an optional standard natural language symbol applicable to the place-value (when omitted the language applicable to the page will control), a place-class, one or more place-subclasses if any, and one or more place name parts (where, e.g., in "Cape Town, South Africa", "Cape Town" is a place name part but "Town" is not). Spaces after semicolons and commas are optional; spaces within place-values are present when required for each place-value (e.g., "Quezon City", not an invented "QuezonCity"). To distinguish names that might otherwise be too similar, place-classes, all lower-case and hyphenatably spaceless, include outer-space, region (on Earth and crossing or larger than a nation, e.g., southern hemisphere, polar region, temperate zone, or Asia), intntl-water (an 'international water body'), intntl-agcy ('international agency' or 'international collection', e.g., all U.N. member nations), nation, within-nation (limited to only one political level down from nation, e.g., state, province, territory, possession, city not included within other political units of a nation, or any comparable unit), city (including town, village, hamlet, and any comparable political unit below the level of within-nation), addr (including address, full-length street, building, institution, and neighborhood without political boundaries), pol-unit (pol abbreviating 'political') (e.g., a place of disputed nationhood), hist-pol-unit (hist abbreviating 'historical') (e.g., the Roman Empire), feature (e.g., river), num (e.g., latitude and longitude or outer-space equivalent in numbers), and ethereal (including thealogical/theological, fictional including from modern popular entertainment, and ancient secular mythical, but not including that which is asserted to be a state of mind or existence but not a place, such as nirvana). (Example for one hypothetical page: geographic-coverage="region, sub-Saharan Africa; nation, Panama; city, Panama, Panama; within-nation, Sao Paulo, Brazil; city, Sao Paulo, Sao Paulo, Brazil; within-nation, Mississippi, United States of America; region, Middle East; region, Midwest, United States of America; hist-pol-unit, Northwest Territory, United States of America; feature, river, Indus; outer-space, Indus; ethereal, ultima Thule; ethereal, Heaven; ethereal, Flatland; ethereal, Valhalla; en-US, addr, Hotel Valhalla, Fredrikstad, Norway; es, nation, Espana" (Indus is both a river and a constellation, illustrating the need for place-classes)). Ambiguity of place-values should be avoided despite convenience in coding because search engines may each interpret them as they see fit, e.g., it would be hard for an engine to distinguish New York from New York. For consistency of spelling, several authority lists should be settled upon, with legal, well-known, and disputed names and common abbreviations all being acceptable; but I'm not proposing one here now (relying on IANA's ccTLD list might be too complex to implement and still assure coding consistency, e.g., occasionally ccTLDs can be phased out and off of IANA's list); and promulgating authority lists may best be done publicly by search engine managements, who may disagree with each other. Allowing Unicode for non-Roman alphabet-using locales is desirable, but at present that may raise technical problems, including computer security issues, that are not yet readily soluble.||geography; geography-coverage; geographic; geographical; geographical-coverage||Proposal|
|datetime-coverage||The author may be the best expert on which time frame is most relevant to the content. Leaving that to search engine analysis may be too chancy without search engine optimization, which analysis is difficult to apply by algorithm to, e.g., historical papers that may focus on the 1800s but mention 1731 and 1912 perhaps unimportantly. The value for this keyword is a date or time -- not a range and not vague, for which other keywords are proposed -- in a format in accordance with http://www.w3.org/TR/NOTE-datetime (albeit a note that's at W3C only for discussion). Any of the six levels of granularity in that note are acceptable, such as expressing only a year. Multiple values may be comma-separated and, if this keyword appears more than once within the head element, all the values so appearing are determinative.||dates; date-coverage; dates-coverage; times; time-coverage; times-coverage; era||Proposal|
|datetime-coverage-start||This is identical to the keyword datetime-coverage except that it represents only the start. If this keyword is used without datetime-coverage-end (also proposed), its value is interpreted as starting a range without an end. This keyword and datetime-coverage-end may be used in the same or separate meta tags. The order of the keywords or the tags containing them doesn't matter. Should this keyword appear more than once, only the first one so appearing is determinative.||dates-start; date-coverage-start; dates-coverage-start; times-start; time-coverage-start; times-coverage-start; era-start||Proposal|
|datetime-coverage-end||This is identical to the keyword datetime-coverage except that it represents only the end. If this keyword is used without datetime-coverage-start (also proposed), its value is interpreted as ending a range without a start. This keyword and datetime-coverage-start may be used in the same or separate meta tags. The order of the keywords or the tags containing them doesn't matter. Should this keyword appear more than once, only the first one so appearing is determinative.||dates-end; date-coverage-end; dates-coverage-end; times-end; time-coverage-end; times-coverage-end; era-end||Proposal|
|datetime-coverage-vague||This is identical to the keyword datetime-coverage except that its value is not necessarily crisp. This keyword should be used only when datetime-coverage, datetime-coverage-start, and datetime-coverage-end are inappropriate, but there's no ban on using all four. Any text can be the value (e.g., Pleistocene, 1820s, Tuesdays, or before we were born). If this keyword is used with datetime-coverage, datetime-coverage-start, or datetime-coverage-end, the vague value is to be exploited along with the value/s for the other keyword/s. This keyword and datetime-coverage, datetime-coverage-start, and datetime-coverage-end may be used in the same or separate meta tags. The order of the keywords or the tags containing them doesn't matter. Should this keyword appear more than once within the head element, all are determinative.||dates-vague; date-coverage-vague; dates-coverage-vague; times-vague; time-coverage-vague; times-coverage-vague; era-vague||Proposal|
|author||Searching for one page author's Web work requires a standard robot-parsable format for the information. A personal name, institutional name, or other text entry is permissible. One element or one keyword represents only one author. Multiple authors are to be represented with multiple keywords in the tag or multiple tags. Search engines may index by any component of a name, so a page author need only enter a name once in one first-last or family-given order (e.g., Chris Ng or Ng, Chris, but not requiring both).||page-author||Proposal|
|creator||Searching for one content creator's work requires a standard robot-parsable format for the information. A personal name, institutional name, or other text entry is permissible. One element or one keyword represents only one creator. Multiple creators are to be represented with multiple keywords in the tag or multiple tags. Search engines may index by any component of a name, so a content creator need only enter a name once in one first-last or family-given order (e.g., Pat Thunderbird or Thunderbird, Pat, but not requiring both).||content-creator||Proposal|
|publisher||Searching for one content or page publisher's work requires a standard robot-parsable format for the information. This often differs from creator or author when the publisher is an institution. An institutional name, personal name, or other text entry is permissible. One element or one keyword represents only one publisher. Multiple publishers are to be represented with multiple keywords in the tag or multiple tags, although multiple publishers are less common than multiple authors or creators; multiplicity is more likely for a legal name and a well-known name. Search engines may index by any component of a name, so a publisher need only enter a name once in one order.||Proposal|
|rights||As a page effectively appears in at least two forms, usually one as interpreted and displayed on a device and the other as source code, arguably intellectual property rights that must be asserted must be asserted in ways understandable in both contexts. For example, an uninterpreted © is a raw representation that may legally fail as part of copyright notice to someone seeing source code and not the display, important when someone wants to copy source code for use elsewhere and may rely on a defense of innocent infringement. While such assertions can be made in a comment element, it may be helpful to have a tag that search engines can parse and index verbatim. The value is Unicode text, and may include standard and nonstandard notices, invocations of licenses such as GFDL and ASCAP. and any other information. ASCII text would not suffice when a name or notice legally may have to be in a non-Roman alphabet, but no alternative may yet exist in HTML5. Search engine storage may impose a length limit, but, because of legal consequences, if the value's length exceeds a given limit the search index should retain or interpret none of it but only refer to it. For the synonymy, IP, IP-rights, and IP-right are not reserved; while the abbreviation IP 'intellectual property' is common among attorneys in the U.S., page authors will more likely be computerate, and the abbreviation may be wanted for 'Internet Protocol'.||copyright; right; patent; trademark; service-mark; license; licensing; intellectual-property; intellectual-property-rights; intellectual-property-right||Proposal|
|addmark||The HTML5 mark element appears able to support insertion of markup by either the user's server or third-party intermediate servers as a way of advertising on, commenting on, restyling, or hiding website content without the website owner's knowledge or consent and perhaps without the user's knowledge or consent, either. Therefore, a page author should be able to prevent the adding of a mark element not already in a page. The addmark keyword with a value of "false" meets that need. (A value of "true" is trivial, being identical in meaning to the absence of the keyword.)||W3C Bug 6774||Proposal|
|addmarklocal||This complements the addmark keyword, separately proposed. A page author might want to allow -- only locally -- the adding of a mark element not already in a page. The addmarklocal keyword with a value of "true" meets that need. (A value of "false" when addmark="false" is trivial, being identical in meaning to the absence of the addmarklocal keyword.) Once addmarklocal is written into a page, how it is implemented is beyond the scope of HTML; for example, a particular intranet for whom the author works might look for the keyword and implement it as it sees fit. The author is to recognize the risk inherent in that nothing bars a nonlocal user agent or server from using addmarklocal to reverse addmark, other than that the HTML5 standard as extended by this Wiki bars it, but arguably only well-behaved user agents can be counted on to obey that.||W3C Bug 6774||Proposal|
|MSSmartTagsPreventParsing||Microsoft introduced into Internet Explorer 6 Beta a feature that some website designers wished to preclude from applying in order to prevent public misunderstanding of their websites. The feature allowed a browser to add information but at a risk that users wouldn't know that it wasn't supplied by the website. This keyword was provided by Microsoft for those of us who wanted it. Its value was "TRUE". Microsoft spelled the keyword with some capitals and the value in all capitals but whether capitalization was required for either is unknown; some opinions vary. Microsoft has apparently removed this instruction from its website on the ground that the beta version is no longer available and is not supported, but that doesn't assure that some users aren't still using the beta browser, perhaps inadvertently. Therefore, designers may wish to continue using the keyword and value and they are preserved here.||e.g., The Register (U.K.), Univ. Oregon (U.S.) (PDF p. 18), & John Chambers (U.S.) (job résumé near root), all as accessed 4-19-09||Proposal|
|Keyword||Brief description||Link to more details||Synonyms||Status|
|cache||Value must be "public", "private", or "no-cache". Intended as a simple way to tell user agents whether to store a copy of the document or not. An alternate for HTTP/1.1's cache-control; for publishers without access to modifying cache-control.
This doesn't actually work; use HTTP headers instead.
|keywords||A comma-separated list of keywords that describe this page. Not very necessary these days; search engines use much more sophisticated means to determine the page's contents.||none||Unendorsed|
For the "Status" section to be changed to "Accepted", the proposed keyword must either have been through the Microformats process, and been approved by the Microformats community; or must be defined by a W3C specification in the Candidate Recommendation or Recommendation state. If it fails to go through this process, it is "Unendorsed".
For more details, see the HTML5 specification.