Specification For HTML Meta Element with Name Value Subject-Datetime

Section 1: Introduction

This is the specification for the HTML meta element with the name attribute value set to “subject-datetime”. This is version 1.0.3 of this specification.

HTML is the HyperText Markup Language, which is a commonly used, perhaps the most commonly used, non-natural language for pages hosted on the World Wide Web. HTML is generally written approximately in accordance with specifications that have been revised several times. Two of those HTML specifications are the HTML Living Standard (as updated May 13, 2017 and May 16, 2017 (One-Page Version treated here as if authoritative) (<https://html.spec.whatwg.org/>, as accessed May 13, 2017 and May 16, 2017)) and HTML 5.1 (version of November 1, 2016) (<http://www.w3.org/TR/html51/single-page.html>, as accessed before and on May 16, 2017). The HTML Living Standard is maintained by the Web Hypertext Application Technology Working Group (WHATWG) and HTML 5.1 is maintained by the World Wide Web Consortium (W3C). Each of those HTML specifications specifies numerous elements and, in section 4.2.5 of each such HTML specification, one such element is the meta element. For that element, each of those HTML specifications specifies attributes including the name attribute, specifies some names that can be values for that attribute (limited to one such value per such attribute per such element), and provides, in section 4.2.5.2 of each such HTML specification, a means by which extensional or additional names may be proposed to be values for that attribute, each such proposal to include a link to a specification for that extensional or additional name. This specification may appropriately be linked to from such a proposal.

This specification, as published on this page and which, except as otherwise stated, is normative, shall also apply, insofar as compatible, to any specification of the HTML Living Standard or of HTML 5.1 other than those referenced above and of any version preceding or succeeding HTML 5.1; except that it shall not apply to any page authored before this specification was first published (the date of such first publication being stated below).

Sec. 1.1: Definitions and Construction

The words and phrases must, must not, required, shall, shall not, should, should not, recommended, may, and optional in this specification and regardless of capitalization are to be interpreted as described in RFC 2119 (also known as BCP 14).

In this specification, if a string, including a null string and a non-null string with no visible or displaying characters, is rendered (including being displayed) with or surrounded by single quotation marks which are curved when a font in which this specification may be displayed has single quotation marks as both straight and curved or is rendered (including being displayed) with or surrounded by double quotation marks which are curved when a font in which this specification may be displayed has double quotation marks as both straight and curved, then the quotation marks that may thus be curved are, unless otherwise stated in this specification, not part of the string. Thus, generally, the string represented by “example” is only seven characters long, not nine.

In examples in this specification, closing slashes are provided only for convenience and are not required where not required by HTML.

Sec. 1.2: Problem Being Solved

This subsection is non-normative.

A page may be largely about an event or a situation for which a particular datetime is or ranges of explicit and implicit datetimes are an important part of the subject, perhaps but not necessarily that it is new. Ranges might be continuous or discontinuous. An implicit datetime range that’s approximate might be appropriate for an archaeological period, for example. Datetimes might for a range or might be nonadjacent. Not all datetimes mentioned in a page’s content might be within a page content’s subject. For a search engine to extract the relevant datetimes from the plain text may be difficult and may produce unreliable results. For example, a person may have granted a once-in-a-lifetime interview in 1992 in which the person described events in 1955, and because the interview itself was so much in demand and so difficult to get the prominence may be perceived by a search engine as belonging to 1992 when the page author may have intended that it be associated with 1955. The author may have a reason for promoting 1992 for the page when viewed at first but may want it to come up in searches for the subject events occurring in 1955. If the page is primarily a verbatim transcript of the interview and the person only implied 1955 so that the year is identifiable only from dense context, and it is not in the website publisher’s interest to rewrite the interview because that would make it not verbatim, a search engine may fail to extract the appropriate year. If the person explicitly referenced other years for contrast, a search engine may see those dates but not realize that they’re present only for contrast and are not the main year of the subject. Therefore, a robot-parsable format is needed, to be used at the page author’s discretion.

A page may be frequently or recently updated although the content may be about a subject that is old. This may be due to unrelated edits to the source code, such as if the page acquires a new look to cconform to changes elsewhere in a website or if technical edits provide conformance to a change in HTML. This may confuse a search engine into presenting a result for the page as if it was newly revised when what is new about it is not the subject content. A page author therefore may want a way to reduce irrelevant traffic and to aid search engines in prioritizing the page in search results when it is likely to be more relevant to searchers’ interests.

Sec. 2: Method

Sec. 2.1: Single Element

There may be an HTML meta element with the name attribute value set to “subject-datetime” and, if that element is present, it shall have the content attribute value set to one and only one of the following values, which shall not have diacritical marks and which shall be parsed caselessly:

Sec. 2.1.1: Point in Time or Predefined Range

Sec. 2.1.1.1: Datetime of a Year or Less

Examples are non-normative.

Sec. 2.1.1.1.1: Other than Quarter

Sec. 2.1.1.1.1.1: Gregorian

Non-normatively, it is noted that a date that is in accordance with the Gregorian calendar is sometimes annotated as New Style (N.S.), in contrast to Old Style (O.S.), which is an annotation for a date that is in accordance with the Julian calendar. The Gregorian calendar now is predominantly used in many nations and, normatively, is the basis of datetimes in this specification unless otherwise represented.

For a datetime in C.E. (‘Common Era’) or A.D. (‘Anno Domini’), the value shall be a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity and with nothing appended.

Example:

For a datetime in B.C.E. (‘Before (the) Common, Current, or Christian Era’) or B.C. (‘Before Christ’), the value shall be a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity and with “-bce” appended.

Example:

For a datetime in A.D.A. (‘After the Development of Agriculture’), the value shall be a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity and with “-ada” appended. Non-normatively, it is noted that year 1 A.D.A. is only approximately equivalent to a given year B.C.E.

Example (as equivalent to 2017 C.E.):

Sec. 2.1.1.1.1.2: Other than Gregorian

For a year on a Julian or O.S. (‘Old Style’) calendar, the value shall be a string formed as “cal-julian-. . .” in which the ellipsis shall be replaced with a year formed as a positive integer.

Example:

For a year in A.M. (‘Anno Mundi’), including for use with the Hebrew or Jewish calendar, the value shall be a string formed as “am-. . .” in which the ellipsis shall be replaced with a year formed as a positive integer.

Example:

For a year in A.H. (‘Anno Hegirae’), viz., on a Hijri, Muslim, or Islamic calendar, the value shall be a string formed as “. . .-ah” in which the ellipsis shall be replaced with a year formed as either a positive integer or one of the following spaceless strings representing unnumbered years in the order here listed, which order chronologically starts with the earliest: “permission”, “orderoffighting”, “trial”, “congratulationonmarriage”, “earthquake”, “enquiring”, “gainingvictory”, “equality”, “exemption”, and “farewell”.

Examples:

For a year in B.H. (‘Before the Hijra’), viz., on or relative to a Hijri, Muslim, or Islamic calendar, the value shall be a string formed as “. . .-bh” in which the ellipsis shall be replaced with a year formed as a positive integer.

Example:

For a year on a Bikrami (or Vikrami or Hindu) calendar, the value shall be a string formed as “cal-bikrami-. . .” in which the ellipsis shall be replaced with a year formed as a positive integer.

Example:

For a year on a Bengali (or Bangla, Bônggabdô, or Banggabda) calendar, the value shall be a string formed as “cal-bengali-. . .” in which the ellipsis shall be replaced with a year formed as a positive integer which may be followed by either “-new” or “-old”. The calendar revision adopted in Bangladesh in 1987 is referred to by the “-new”. If neither “-new” or “-old” is part of the value, a user agent shall infer “-new”.

Examples (these are not intended to represent the same year):

Sec. 2.1.1.1.2: Quarter

For a quarter of a year in C.E. (‘Common Era’) or A.D. (‘Anno Domini’), the value shall be a string formed as a four-digit positive integer with “q1”, “Q1”, “q2”, “Q2”, “q3”, “Q3”, “q4”, or “Q4”, spacelessly and hyphenlessly appended and except that the integer may be less than four digits long for a year preceding the year 1000.

Examples:

Sec. 2.1.1.2: Decade

For a decade in C.E. (‘Common Era’) or A.D. (‘Anno Domini’), the value shall be a string formed as a four-digit positive integer with “s” spacelessly and hyphenlessly appended, of which integer the units digit of the first year shall be 0, and except that the integer may be less than four digits long for a year preceding the year 1000 and for a year preceding the year 10 the integer shall be 00.

Examples:

For a decade in B.C.E. (‘Before (the) Common, Current, or Christian Era’) or B.C. (‘Before Christ’), the value shall be a string formed as a four-digit positive integer with “s-bce” spacelessly appended, of which integer the units digit of the first year shall be 0, and except that the integer may be less than four digits long for a year following the year 1000 B.C.E. and for a year following the year 10 B.C.E. the integer shall be 00.

Example:

For a decade in A.D.A. (‘After the Development of Agriculture’), the value shall be a string formed as a four-digit positive integer with “s-ada” spacelessly appended, of which integer the units digit of the first year shall be 0, and except that the integer may be less than four digits long for a year preceding the year 1000 A.D.A. and for a year preceding the year 10 A.D.A. the integer shall be 00. Non-normatively, it is noted that year 1 A.D.A. is only approximately equivalent to a given year B.C.E.

Example:

Sec. 2.1.1.3: Century

For a century in C.E. (‘Common Era’) or A.D. (‘Anno Domini’), the value shall be a string formed as “century-. . .” in which the ellipsis shall be replaced by a positive integer representing a century and omitting the tens digit and the units digit and for which century the implied units digit of the first year shall be 0.

Example:

For a century in B.C.E. (‘Before (the) Common, Current, or Christian Era’) or B.C. (‘Before Christ’), the value shall be a string formed as “century-. . .-bce” in which the ellipsis shall be replaced by a positive integer representing a century and omitting the tens digit and the units digit and for which century the implied units digit of the first year shall be 0.

Example:

For a century in A.D.A. (‘After the Development of Agriculture’), the value shall be a string formed as “century-. . .-ada” in which the ellipsis shall be replaced by a positive integer representing a century and omitting the tens digit and the units digit and for which century the implied units digit of the first year shall be 0. Non-normatively, it is noted that year 1 A.D.A. is only approximately equivalent to a given year B.C.E.

Example:

Sec. 2.1.1.4: Millennium

For a millennium in C.E. (‘Common Era’) or A.D. (‘Anno Domini’), the value shall be a string formed as “mill-. . .” in which the ellipsis shall be replaced by a positive integer representing a millennium and omitting the hundreds digit, the tens digit, and the units digit, counting millennia such that the years 1–1000 or 0–999 constitute millennium 1.

Example:

For a millennium in B.C.E. (‘Before (the) Common, Current, or Christian Era’) or B.C. (‘Before Christ’), the value shall be a string formed as “mill-. . .-bce” in which the ellipsis shall be replaced by a positive integer representing a millennium and omitting the hundreds digit, the tens digit, and the units digit, counting millennia such that the years 1–1000 B.C.E. or 0–999 B.C.E. constitute millennium 1.

Example:

For a millennium in A.D.A. (‘After the Development of Agriculture’), the value shall be a string formed as “mill-. . .-ada” in which the ellipsis shall be replaced by a positive integer representing a millennium and omitting the hundreds digit, the tens digit, and the units digit, counting millennia such that the years 1–1000 A.D.A. or 0–999 A.D.A. constitute millennium 1. Non-normatively, it is noted that year 1 A.D.A. is only approximately equivalent to a given year B.C.E.

Example:

Sec. 2.1.1.5: Floating Datetime

For a floating datetime in C.E. (‘Common Era’) or A.D. (‘Anno Domini’) (a floating datetime being a ‘datetime or range that floats within a longer datetime range’), the value shall be a string formed as “float-. . .-. . .” in which the first ellipsis shall be replaced by one and only one name of a floating datetime or range, which name should be one generally recognized in popular or scholarly discourse (such as that in folk belief, theology, or astronomy) and which name shall be stated in this value spacelessly and in which the second ellipsis shall be replaced by one and only one datetime expressed as a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity. Certain seasons and holidays, represented here by the following strings, shall be among such ranges that float: “spring”, “summer”, “fall”, “autumn”, “winter”, “rainyseason”, “dryseason”, and “easter”; “fall” and “autumn” shall have the same meaning. Non-normatively, seasons are here treated as not bounded by specific dates worldwide as no law so bounding may have been promulgated everywhere in the world; the seasons are therefore here treated as floating worldwide.

Examples (for Easter, 1986, and for the day of the full moon in February, 1813, respectively):

For a floating datetime in B.C.E. (‘Before (the) Common, Current, or Christian Era’) or B.C. (‘Before Christ’) (a floating datetime being a ‘datetime or range that floats within a longer datetime range’), the value shall be a string formed as “float-. . .-. . .-bce” in which the first ellipsis shall be replaced by one and only one name of a floating datetime or range, which name should be one generally recognized in popular or scholarly discourse (such as that in folk belief, theology, or astronomy) and which name shall be stated in this value spacelessly and in which the second ellipsis shall be replaced by one and only one datetime expressed as a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity. Certain seasons and holidays, represented here by the following strings, shall be among such ranges that float: “spring”, “summer”, “fall”, “autumn”, “winter”, “rainyseason”, “dryseason”, and “easter”; “fall” and “autumn” shall have the same meaning. Non-normatively, seasons are here treated as not bounded by specific dates worldwide as no law so bounding may have been promulgated everywhere in the world; the seasons are therefore here treated as floating worldwide.

Example (for the day of the full moon in February, 1813, B.C.E.):

For a floating datetime in A.D.A. (‘After the Development of Agriculture’) (a floating datetime being a ‘datetime or range that floats within a longer datetime range’), the value shall be a string formed as “float-. . .-. . .-ada” in which the first ellipsis shall be replaced by one and only one name of a floating datetime or range, which name should be one generally recognized in popular or scholarly discourse (such as that in folk belief, theology, or astronomy) and which name shall be stated in this value spacelessly and in which the second ellipsis shall be replaced by one and only one datetime expressed as a string formed in accordance with http://www.w3.org/TR/NOTE-datetime with any level of granularity. Certain seasons and holidays, represented here by the following strings, shall be among such ranges that float: “spring”, “summer”, “fall”, “autumn”, “winter”, “rainyseason”, “dryseason”, and “easter”; “fall” and “autumn” shall have the same meaning. Non-normatively, seasons are here treated as not bounded by specific dates worldwide as no law so bounding may have been promulgated everywhere in the world; the seasons are therefore here treated as floating worldwide. Non-normatively, it is noted that year 1 A.D.A. is only approximately equivalent to a given year B.C.E.

Example (for the day of the full moon in February, 6813, A.D.A.):

Sec. 2.1.1.6: Light-Years

Non-normatively, it is noted that while a light-year is a measure of distance it is also a measure of time, because light travels at a finite speed. Non-normatively, this is relevant to cosmology and astronomy.

For a date light-years in the past, the value shall be a string formed as either “light-. . .” or “light-. . .-past” in which the ellipsis shall be replaced by one and only one positive integer spacelessly followed by either “mly” (‘mega light-years’ for millions of light-years ago) or “gly” (‘giga light-years’ for billions of light-years ago) and in which both formations have the same meaning.

For a date light-years into the future, the value shall be a string formed as “light-. . .-future” in which the ellipsis shall be replaced by one and only one positive integer spacelessly followed by either “mly” (‘mega light-years’ for millions of light-years ago) or “gly” (‘giga light-years’ for billions of light-years ago).

Examples:

Sec. 2.1.1.7: Period Usually Multiple Years Long

For a period (of the kind usually years long and usually imprecisely defined as to which years are boundaries), the value shall be a string formed as “period-. . .” in which the ellipsis shall be replaced by one and only one name of a period, which name should be one recognized in scientific consensus (such as that in cosmology, geology, or archeology), and which name shall be stated in this value spacelessly and with only a-z and 0-9 (thus, letters may only be in lower case).

Example (for Çatal Höyük):

Sec. 2.1.2: Arbitrary Range

A value specified in >section 2.1.1 is a subvalue for the purpose of this subsubsection (2.1.2).

A value that consists of a subvalue followed by two hyphens followed by a subvalue represents a range of time from the chronologically earlier of the two subvalues to the chronologically later of the two subvalues, inclusive, regardless of the order of appearance in the value of the two subvalues; except that if which subvalue is the chronologically earlier cannot be determined with certainty then the subvalue appearing first in the value shall be presumed to be the chronologically earlier of the two subvalues. Non-normatively, authors should accept that, while an author or a creator may see no ambivalence as to which subvalue is the chronologically earlier because the author or creator might possess specialized knowledge or an informed opinion, a programmer or manager of a user agent might not have that same knowledge or opinion and the result may be an unexpected parsing of the value; therefore, an author should be careful in determining which subvalue is the chronologically earlier in order to place it to precede the other subvalue in the value.

Where two hyphens separate two subvalues or precede or follow a subvalue, spaces between the hyphens or separating either hyphen from a subvalue shall be ignored.

A value that consists of only two hyphens followed by a subvalue represents a range of time from the beginning of all time to that represented by the subvalue, inclusive.

A value that consists of “universe” (without quotation marks) followed by two hyphens followed by a subvalue represents a range of time from the beginning of the universe in which we exist and with the beginning to be in accordance with scientific consensus at the time of parsing by a user agent to that represented by the subvalue, inclusive.

A value that consists of a subvalue not in the future followed only by two hyphens represents a range of time from that represented by the subvalue to the present, inclusive, where the present is as determined, explicitly or implicitly, by the user agent.

A value that consists of a subvalue in the future followed only by two hyphens represents a range of time from that represented by the subvalue into the infinite future, inclusive.

A value that consists of a subvalue followed by two hyphens followed by “infinite” (without quotation marks) represents a range of time from that represented by the subvalue to the infinite future, inclusive.

A value that consists of only two hyphens represents the range of all time, including the longer in each direction of theological and scientific.

A value that consists of only “universe” (without quotation marks) represents a range of time from the beginning of the universe in which we exist to the end of that universe, both times in accordance with scientific consensus at the time of parsing by a user agent.

Examples:

Sec. 2.2: Values Not Directly Provided

This subsection is non-normative.

Some kinds of values are not directly provided but possibly may be indirectly provided for. The following are examples:

— A datetime in a fiscal year in the U.S. may be converted to a datetime in C.E. (or A.D.) or B.C.E. (or B.C.).

— A datetime in a calendar based on eras or the reigns of emperors or other significant entities may perhaps be converted to a datetime in C.E. (or A.D.) or B.C.E. (or B.C.).

— A datetime in B.P. (‘Before Present’), which refers to time measured backward from 1950 by analysis of radioactive decay of a chemical constituent of a substance, may perhaps be converted to a datetime in C.E. (or A.D.) or B.C.E. (or B.C.), although the method of conversion may depend on the chemical and the date of the analysis (due to the consensus of scientific knowledge on that date) and may not be simple.

— A datetime preceding the inception of time as measured or adjudged in a system that may not acknowledge time before that inception although such earlier time did occur may, if evidence or reasonable speculation on such datetime is available, perhaps be converted to a datetime in C.E. (or A.D.) or B.C.E. (or B.C.).

Sec. 2.3: Multiple Elements

More than one HTML meta element with the name attribute value set to “subject-datetime” may be provided, in which case all are determinative. For example, non-normatively, a page about the start and the end of a war, but not about the middle, might have the following two elements in the same page:

With that example, a search engine with a request for pages on the war should treat the result as high for the page with this markup if the request was for 1939, 1945, or both, but not as high if the request was for 1939 to 1945 and even lower if the request was for 1938, 1940 to 1944, or 1946, even if the latter years are incidentally mentioned in brief parts of the page content.

Sec. 2.4: Explanations

This subsection is non-normative.

When the content attribute value is the same for more than one date range, such as when the decade of the 1770s may represent either 1770–1779 or 1771–1780, this specification so permits more than one not as if both are equally correct for the purpose but because popular beliefs accept both for the purpose and this element with this name is likely to be added by many authors who may disagree with each other on the point.

The content attribute value is generally not a value with three or more consecutive zeros (such as 0000s, 1000s, 2000s, or 3000s) without a textual string prepended to it, because of reasonable confusion because such a value could represent a millennium, a century, or a decade, each of which may instead be more clearly represented in a way provided for in this specification.

Sec. 2.5: Proposals Welcome

This subsection is non-normative except as otherwise stated.

Proposals for fulfilling the purpose of this specification where the subject of a page depends on a calendar or other system of counting dates or time not explicitly encompassed or not adequately encompassed by this specification are welcome and may be submitted to a current author or editor of this specification through contact information perhaps available on or through this page. An example might be a calendar unique to a nation, industry, or cultural group and if there is likely to be a benefit from the application of this specification.

Sec. 3: Security, Synonymy, History, and Backwards Compatibility

This section is non-normative except as otherwise stated.

Sec. 3.1: Security

No security implication has been identified with respect to this specification.

Sec. 3.2: Synonymy

Normatively, an HTML meta element with the name attribute value set to “page-datetime” is exactly synonymous with an HTML meta element with the name attribute value set to “subject-datetime”.

Normatively, an HTML meta element with the name attribute value set to “page-datetime”, “page-datetime-start”, “page-datetime-end”, or “page-datetime-vague” is approximately synonymous with an HTML meta element with the name attribute value set to “subject-datetime”.

Sec. 3.3: History

Sec. 3.3.1: Subject-Datetime

The original author and editor of this specification, except as otherwise stated, was Nick Levinson, who can be contacted through a link on this page.

Version 1 of this specification was published on this page on December 2, 2017. Version 1 was revised into version 1.0.1, published on December 9, 2017. Version 1.0.1 was revised into version 1.0.2, published on August 23, 2018. Version 1.0.2 was revised into this version, being published on November 6, 2022.

Sec. 3.3.2: Page-Datetime

The name attribute value of this meta element was changed to “subject-datetime” because of the specification author’s concern that a previous name attribute value, “page-datetime”, could be widely misunderstood as referring to when the page’s HTML was created rather than the datetimes relevant to the subject of the page, the latter being the specification author’s original intention.

Sec. 3.3.3: Datetime-Coverage, Datetime-Coverage-Start, Datetime-Coverage-End, and Datetime-Coverage-Vague

The name attribute value of this meta element, “subject-datetime”, was preceded at initiation by a set of name attribute values of this meta element, “datetime-coverage”, “datetime-coverage-start”, “datetime-coverage-end”, and “datetime-coverage-vague”, which collectively had functionality similar to that of the name attribute value of this meta element for which this specification is now normative, “subject-datetime”. Page authors should use “subject-datetime” rather than “datetime-coverage”, “datetime-coverage-start”, “datetime-coverage-end”, or “datetime-coverage-vague” as a name attribute value.

Sec. 3.3.3.1: Datetime-Coverage

Sec. 3.3.3.2: Datetime-Coverage-Start

Sec. 3.3.3.3: Datetime-Coverage-End

Sec. 3.3.3.4: Datetime-Coverage-Vague

Sec. 3.4: Backwards Compatibility

Sec. 4: Intellectual Property For This Specification

Sec. 4.1: Copyright Status

Insofar as lawful, with respect to the CC0 1.0 Universal legal tool (herein “CC0”) (summarized at https://creativecommons.org/publicdomain/zero/1.0/) (both URLs as accessed November 26, 2017) of the Creative Commons Corporation, Nick Levinson, the original author and editor of this specification, has, upon first publication of this specification, hereby become the Affirmer under CC0 and hereby elected to apply CC0 to this specification, to publicly distribute this specification, and to make this specification available, all such electing as provided for in CC0, and hereby waived, abandoned, surrendered, granted, affirmed, offered, and disclaimed, all such waiving, abandoning, surrendering, granting, affirming, offering, and disclaiming being with respect to this specification and being as provided for in CC0.

Sec. 4.2: Trademarks, Endorsements, and Associations

“Creative Commons” is a trademark of Creative Commons Corporation; use of such trademark does not imply endorsement by or association with Creative Commons Corporation.

“CC0” is a trademark of Creative Commons Corporation; use of such trademark does not imply endorsement by or association with Creative Commons Corporation.

Sec. 4.3: Other Claims

Except as otherwise referenced, the original author and editor of this specification, Nick Levinson, is not aware of any claim by any other person or entity to intellectual property adversely affecting this specification.

Sec. 5: Section Titles Not Restrictive

Titles of sections, including subsections at all subsectional depths, are provided solely for convenience and do not restrict the meaning of the content of the respective sections. Titles of sections include headlines of sections.