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Time element

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Revision as of 13:00, 6 August 2010 by Pigsonthewing (talk | contribs) (Choose different default date: c)
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Research, data, use cases, issues, and enhancements related to the HTML5 time element.


year only

The time element should accept just a year.

ISO8601 syntax
use case research

Opinions / discussion:

year month only

The time element should accept just a year and a month.

ISO8601 syntax
use cases
Blog/publishing archive pages - see Benward.me, ablognotlimited.com (need specific links to archive pages), http://www.flickr.com/photos/tantek/archives/
output equivalent of <input type="month">, see impedance match new date time inputs above.

Opinions / discussion:

year week only

The time element should accept just a year and a week number.

ISO8601 syntax
use case research
no examples in the wild currently. If anyone knows of any sites which publish references to specific weeks of a year, either by name / expression (e.g. "first week of the year") or by specific number (e.g. "weeks 1-26"), please provide URLs and quotes of example content.
output equivalent of <input type="week">, see impedance match new date time inputs above.
to provide the output equivalent of <input type="week">

See impedance match new date time inputs above.

Opinions / discussion:

  • +1 Tantek per good design of impedance matching date time inputs.
  • ...

month day only

The time element should accept just a month and a day.

ISO8601 syntax
use case research

Opinions / discussion:

composite nested time elements

A time element should permit child time elements which may contain only partial date time information which can then be composed into more complete date time information.

This is intended as a cleaner way to provide functionality equivalent to the microformats value-class-pattern date and time values pattern.

Simple example:

Currently the <time> element forces you to duplicate and hide date time information if you want to avoid displaying the not-very-friendly full ISO datetime:

<p class="vevent">
  <span class="summary">I went to the cafe</span> at 
  <time class="dtstart"
        datetime="2010-08-05T18:00:00">18:00 on 2010-08-05</time>.

Note the date and time information is duplicated (violating DRY, placing the content at risk of divergence).

With the microformats value-class-pattern date and time values pattern you could instead mark this up like this:

<p class="vevent">
  <span class="summary">I went to the cafe</span> at 
  <span class="dtstart">
     <span class="value">18:00</span> on 
     <span class="value">2010-08-05</span>

Advantages: no duplication of time and date data! (avoiding DRY violation) If you need to update the info, you only have to update it in one place, thus reducing the chances of inforot.

Disadvantage: the loss of the HTML5 time semantic.

We'd like to have our time and date time separation as well, so this should work:

<p class="vevent">
  <span class="summary">I went to the cafe</span> at 
  <time class="dtstart">
     <time>18:00</time> on 

In short: the algorithm for determining the "datetime" of a time element should:

  1. check for an explicit 'datetime' attribute (allowing a local to element override regardless of child elements)
  2. check for nested <time> elements, and if any are found, compose their values into a more complete date and time (use the first date found if any, then the first time found, if any. thus latter dates or times are gracefully ignored)
  3. use the complete contents of the <time> element as its datetime value.

Essentially, step 2 is added to enable composing nested child time elements.

Opinions / discussion:

  • +1 Tantek - I'd really like to be able to more cleanly markup dates and times than the best we have been able to do so far with microformats (the aforementioned value-class-pattern), and HTML5 presents us with the potential to do so.
  • -1 Andy Mabbett - Introduces excessive complexity on the apparent assumption that a significant proportion of dates in the wild (or even in microformats in the wild) use the format "2010-08-05" and not more human-readable and accessible prose such as, say, "5 August 2010" or "August 5th, 2010". No evidence (also supposedly required by the microformats "process") has been provided to show that this is the case. {If the apparent assumption is not made, then this fails 80/20.)
  • ...

am pm and coarser time parsing

Right now time values inside a <time> element are required specify hours in 24 hour time.

In our experience with the microformats value class pattern date and time values we've found it is relatively easy to both specify and implement (multiple implementations) parsing of (potentially coarser) am and pm values to permit a broader set of values to marked up directly (rather than with a separate datetime/title attribute).

In short, the current <time> element only allows for the following pattern:

  • HH:MM:SS - where HH is in 24 hour time.

This proposal expands this to:

  • HH:MM:SSam
  • HH:MM:SSpm
  • HH:MMam
  • HH:MMpm
  • HHam
  • HHpm

Where "am" and "pm" mean "am or a.m." and "pm or p.m." with optional leading ("6 pm") and intermittent ("6 p. m.")white-space; and are case-insensitive ("6 PM").

When :SS or :MM:SS is omitted, infer :00 or :00:00, respectively.

Example (uses aforementioned composite time proposal as well)

<p class="vevent">
  <span class="summary">I went to the cafe</span> at 
  <time class="dtstart">
     <time>6pm</time> on 

Opinions / discussion:

  • +1 Tantek - in practice we in the microformats community have found that enabling users to markup am/pm times leads to many more cases where we can avoid violating DRY and thus encourage greater accuracy over time for such content. I think the HTML5 <time> element presents us with the opportunity to more cleanly markup times (than what we've been able to do with the aforementioned microformats value-class-pattern), and thus we should do so.
  • 0(query) Andy Mabbett - How does this cater for "noon" and "midnight", and the ambiguity over "12am" and "12pm"? How does it internationalise? Also, see above for concerns over date formatting.
  • ...

Calendar scale

The time element should accept a calendar scale (CALSCALE; default is GREGORIAN) per (and to facilitate interoperability with) the emergent vCard 4 specification, to allow for the the mark-up of non-Gregorian (e.g. Julian) dates, using one of a set of pre-defined CALSCALE types.


<time datetime="1330-06-01" calscale="julian">1 June 1330</time>

User agents could be instructed to ignore any unrecognised CALSCALE value, treating the contents of the element as plain text for data-processing (but not styling) purposes. This would prevent, for example the processing of the above example by an agent written to deal only with Gregorian dates. (At some point, CSS should recognise CALSCAlE, allowing authors to, say, style all Julian dates differently to Gregorian dates.)

Opinions / discussion:

  • +1 Andy Mabbett (Per use cases in VCARDDAV, EDTF & TEI - see external links)

Fuzzy dates

The time element should accept fuzzy (uncertain, approximate) dates ("around 18 June 1855" "summer 1970", "circa December 1963", "flourished 1580"), centuries, and eras ("Edwardian", "bronze age", "Jurassic")".

Opinions / discussion:

  • +1 Andy Mabbett (Per use cases in "Extended Date Time Format" proposals & TEI - see external links)
    • Uncertainty possibly resolved by a "certainty" attribute:
      <time datetime="1855-06-18" certainty="3days">around 18 June 1855</time>
      <time datetime="1970-06" certainty="45days">summer 1970</time>
      (with "45days" meaning "+/- 45 days" - in other words, a 90-day window, and similar allowance for year or other ranges; or:
      <time datetime="1963-12" certainty="circa">circa December 1963</time>
      with pre-defined prose values allowed, such as "flourished", "notbefore", "notafter", etc.
  • +1 Jim O'Donnell (Dates such as 'circa 1910' published on Flickr eg. The RNVR Training Ship 'Buzzard'… also a list of fuzzy dates for a set of photos.)

Specification ambiguities

The specification requires that time be expressed as UTC (or another time zone with a specified offset from UTC). However, the representation of leap seconds is not specified. Further, the algorithms to convert between string and number are flawed, because the number is described as "number of milliseconds elapsed from midnight UTC on the morning of 1970-01-01" but the actual number of milliseconds includes all kinds of strange decisecond offsets during the period 1961-01-01 to 1972-01-01. Also, UTC did not exist before about 1960.

Unix timekeeping has a long history of terrible definitions, and Unix notions of time should be totally rejected and expunged.

Choose different default date

The statement that valueAsDate IDL attribute should return the value 1970-01-01 plus the appropriate time when the time element contains no date creates a problem that there are likely to be time elements that explicitly contain that date.

A better choice would be a value that is highly unlikely to be encountered, and would be implausible as an actual date in most applications, perhaps 9999-12-31.

Opinions / discussion:

  • 0 (comment) Andy Mabbett - 9999-12-31 may well occur in real applications (projected comet sightings, say). Can we return either an invalid date (perhaps 9999-02-31) or an error code?
  • ...

impedance match new date time inputs

The time element should be able to represent every granularity of times and dates that the new date time <input> elements allow. Here is a list of all the date time <input> elements along with the corresponding <time> element usage (if applicable)

<input type="date">           - <time>YYYY-MM-DD</time>
<input type="datetime">       - <time>YYYY-MM-DDTHH:MM:SS</time>
<input type="month">          - not supported in current time element
<input type="week">           - not supported in current time element
<input type="time">           - <time>HH:MM:SS</time>
<input type="datetime-local"> - <time>HH:MM:SS-ZZ:YY</time>
New proposed input elements:
<input type="year">           - not supported in current time element
<input type="month-day">      - not supported in current time element

In particular the <time> element is missing support for the following date inputs:

In addition, if the new proposed input elements are accepted, the respective time element support should be added as well:

Opinions / discussion:

External links


Blog posts, Twitter updates etc. may be tagged HTML5time or #HTML5time

Prior discussion