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    1. 2.4 Common microsyntaxes
      1. 2.4.1 Common parser idioms
      2. 2.4.2 Boolean attributes
      3. 2.4.3 Keywords and enumerated attributes
      4. 2.4.4 Numbers
        1. 2.4.4.1 Signed integers
        2. 2.4.4.2 Non-negative integers
        3. 2.4.4.3 Floating-point numbers
        4. 2.4.4.4 Lists of integers
      5. 2.4.5 Dates and times
        1. 2.4.5.1 Months
        2. 2.4.5.2 Dates
        3. 2.4.5.3 Yearless dates
        4. 2.4.5.4 Times
        5. 2.4.5.5 Local dates and times
        6. 2.4.5.6 Time zones
        7. 2.4.5.7 Global dates and times
        8. 2.4.5.8 Weeks
        9. 2.4.5.9 Durations
        10. 2.4.5.10 Vaguer moments in time
      6. 2.4.6 Colors
      7. 2.4.7 Space-separated tokens
      8. 2.4.8 Comma-separated tokens
      9. 2.4.9 References
      10. 2.4.10 Media queries

2.4 Common microsyntaxes

There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.

2.4.1 Common parser idioms

The space characters, for the purposes of this specification, are U+0020 SPACE, "tab" (U+0009), "LF" (U+000A), "FF" (U+000C), and "CR" (U+000D).

The White_Space characters are those that have the Unicode property "White_Space" in the Unicode PropList.txt data file. [UNICODE]

This should not be confused with the "White_Space" value (abbreviated "WS") of the "Bidi_Class" property in the Unicode.txt data file.

2.4.2 Boolean attributes

A number of attributes are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If the attribute is present, its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute's canonical name, with no leading or trailing whitespace.

The values "true" and "false" are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether.

Here is an example of a checkbox that is checked and disabled. The checked and disabled attributes are the boolean attributes.

<label><input type=checkbox checked name=cheese disabled> Cheese</label>

This could be equivalently written as this:

<label><input type=checkbox checked=checked name=cheese disabled=disabled> Cheese</label>

You can also mix styles; the following is still equivalent:

<label><input type='checkbox' checked name=cheese disabled=""> Cheese</label>

2.4.3 Keywords and enumerated attributes

Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.

If an enumerated attribute is specified, the attribute's value must be an ASCII case-insensitive match for one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace.

When the attribute is specified, if its value is an ASCII case-insensitive match for one of the given keywords then that keyword's state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, if the attribute value matches none of the keywords but there is a missing value default state defined, then that is the state represented by the attribute. Otherwise, there is no default, and invalid values must be ignored.

When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.

The empty string can be a valid keyword.

2.4.4 Numbers

2.4.4.1 Signed integers

A string is a valid integer if it consists of one or more characters in the range ASCII digits, optionally prefixed with a U+002D HYPHEN-MINUS character (-).

A valid integer without a "-" (U+002D) prefix represents the number that is represented in base ten by that string of digits. A valid integer with a "-" (U+002D) prefix represents the number represented in base ten by the string of digits that follows the U+002D HYPHEN-MINUS, subtracted from zero.

2.4.4.2 Non-negative integers

A string is a valid non-negative integer if it consists of one or more characters in the range ASCII digits.

A valid non-negative integer represents the number that is represented in base ten by that string of digits.

2.4.4.3 Floating-point numbers

A string is a valid floating point number if it consists of:

  1. Optionally, a "-" (U+002D) character.
  2. One or both of the following, in the given order:
    1. A series of one or more characters in the range ASCII digits.
      1. A single "." (U+002E) character.
      2. A series of one or more characters in the range ASCII digits.
  3. Optionally:
    1. Either a "e" (U+0065) character or a "E" (U+0045) character.
    2. Optionally, a "-" (U+002D) character or "+" (U+002B) character.
    3. A series of one or more characters in the range ASCII digits.

A valid floating point number represents the number obtained by multiplying the significand by ten raised to the power of the exponent, where the significand is the first number, interpreted as base ten (including the decimal point and the number after the decimal point, if any, and interpreting the significand as a negative number if the whole string starts with a "-" (U+002D) character and the number is not zero), and where the exponent is the number after the E, if any (interpreted as a negative number if there is a "-" (U+002D) character between the E and the number and the number is not zero, or else ignoring a "+" (U+002B) character between the E and the number if there is one). If there is no E, then the exponent is treated as zero.

The Infinity and Not-a-Number (NaN) values are not valid floating point numbers.

2.4.4.4 Lists of integers

A valid list of integers is a number of valid integers separated by U+002C COMMA characters, with no other characters (e.g. no space characters). In addition, there might be restrictions on the number of integers that can be given, or on the range of values allowed.

2.4.5 Dates and times

In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]

The digits in the date and time syntaxes defined in this section must be characters in the range ASCII digits, used to express numbers in base ten.

2.4.5.1 Months

A month consists of a specific proleptic Gregorian date with no time-zone information and no date information beyond a year and a month. [GREGORIAN]

A string is a valid month string representing a year year and month month if it consists of the following components in the given order:

  1. Four or more digits, representing year, where year > 0
  2. A "-" (U+002D) character
  3. Two digits, representing the month month, in the range 1 ≤ month ≤ 12
2.4.5.2 Dates

A date consists of a specific proleptic Gregorian date with no time-zone information, consisting of a year, a month, and a day. [GREGORIAN]

A string is a valid date string representing a year year, month month, and day day if it consists of the following components in the given order:

  1. A valid month string, representing year and month
  2. A "-" (U+002D) character
  3. Two digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and year year
2.4.5.3 Yearless dates

A yearless date consists of a month and a day, but with no associated year.

A string is a valid yearless date string representing a month month and a day day if it consists of the following components in the given order:

  1. Optionally, two "-" (U+002D) characters
  2. Two digits, representing the month month, in the range 1 ≤ month ≤ 12
  3. A "-" (U+002D) character
  4. Two digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and any arbitrary leap year (e.g. 4 or 2000)

In other words, if the month is "02", meaning February, then the day can be 29, as if the year was a leap year.

2.4.5.4 Times

A time consists of a specific time with no time-zone information, consisting of an hour, a minute, a second, and a fraction of a second.

A string is a valid time string representing an hour hour, a minute minute, and a second second if it consists of the following components in the given order:

  1. Two digits, representing hour, in the range 0 ≤ hour ≤ 23
  2. A ":" (U+003A) character
  3. Two digits, representing minute, in the range 0 ≤ minute ≤ 59
  4. Optionally (required if second is non-zero):
    1. A ":" (U+003A) character
    2. Two digits, representing the integer part of second, in the range 0 ≤ s ≤ 59
    3. Optionally (required if second is not an integer):
      1. A 002E FULL STOP character (.)
      2. One, two, or three digits, representing the fractional part of second

The second component cannot be 60 or 61; leap seconds cannot be represented.

2.4.5.5 Local dates and times

A local date and time consists of a specific proleptic Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, but expressed without a time zone. [GREGORIAN]

A string is a valid local date and time string representing a date and time if it consists of the following components in the given order:

  1. A valid date string representing the date
  2. A "T" (U+0054) character or a U+0020 SPACE character
  3. A valid time string representing the time

A string is a valid normalized local date and time string representing a date and time if it consists of the following components in the given order:

  1. A valid date string representing the date
  2. A "T" (U+0054) character
  3. A valid time string representing the time, expressed as the shortest possible string for the given time (e.g. omitting the seconds component entirely if the given time is zero seconds past the minute)
2.4.5.6 Time zones

A time-zone offset consists of a signed number of hours and minutes.

A string is a valid time-zone offset string representing a time-zone offset if it consists of either:

This format allows for time-zone offsets from -23:59 to +23:59. In practice, however, the range of offsets of actual time zones is -12:00 to +14:00, and the minutes component of offsets of actual time zones is always either 00, 30, or 45.

See also the usage notes and examples in the global date and time section below for details on using time-zone offsets with historical times that predate the formation of formal time zones.

2.4.5.7 Global dates and times

A global date and time consists of a specific proleptic Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, expressed with a time-zone offset, consisting of a signed number of hours and minutes. [GREGORIAN]

A string is a valid global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:

  1. A valid date string representing the date
  2. A "T" (U+0054) character or a U+0020 SPACE character
  3. A valid time string representing the time
  4. A valid time-zone offset string representing the time-zone offset

Times in dates before the formation of UTC in the mid twentieth century must be expressed and interpreted in terms of UT1 (contemporary Earth solar time at the 0° longitude), not UTC (the approximation of UT1 that ticks in SI seconds). Time before the formation of time zones must be expressed and interpeted as UT1 times with explicit time zones that approximate the contemporary difference between the appropriate local time and the time observed at the location of Greenwich, London.

The following are some examples of dates written as valid global date and time strings.

"0037-12-13 00:00Z"
Midnight in areas using London time on the birthday of Nero (the Roman Emperor). See below for further discussion on which date this actually corresponds to.
"1979-10-14T12:00:00.001-04:00"
One millisecond after noon on October 14th 1979, in the time zone in use on the east coast of the USA during daylight saving time.
"8592-01-01T02:09+02:09"
Midnight UTC on the 1st of January, 8592. The time zone associated with that time is two hours and nine minutes ahead of UTC, which is not currently a real time zone, but is nonetheless allowed.

Several things are notable about these dates:

A string is a valid normalized forced-UTC global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:

  1. A valid date string representing the date converted to the UTC time zone
  2. A "T" (U+0054) character
  3. A valid time string representing the time converted to the UTC time zone and expressed as the shortest possible string for the given time (e.g. omitting the seconds component entirely if the given time is zero seconds past the minute)
  4. A "Z" (U+005A) character
2.4.5.8 Weeks

A week consists of a week-year number and a week number representing a seven-day period starting on a Monday. Each week-year in this calendaring system has either 52 or 53 such seven-day periods, as defined below. The seven-day period starting on the Gregorian date Monday December 29th 1969 (1969-12-29) is defined as week number 1 in week-year 1970. Consecutive weeks are numbered sequentially. The week before the number 1 week in a week-year is the last week in the previous week-year, and vice versa. [GREGORIAN]

A week-year with a number year has 53 weeks if it corresponds to either a year year in the proleptic Gregorian calendar that has a Thursday as its first day (January 1st), or a year year in the proleptic Gregorian calendar that has a Wednesday as its first day (January 1st) and where year is a number divisible by 400, or a number divisible by 4 but not by 100. All other week-years have 52 weeks.

The week number of the last day of a week-year with 53 weeks is 53; the week number of the last day of a week-year with 52 weeks is 52.

The week-year number of a particular day can be different than the number of the year that contains that day in the proleptic Gregorian calendar. The first week in a week-year y is the week that contains the first Thursday of the Gregorian year y.

A string is a valid week string representing a week-year year and week week if it consists of the following components in the given order:

  1. Four or more digits, representing year, where year > 0
  2. A "-" (U+002D) character
  3. A "W" (U+0057) character
  4. Two digits, representing the week week, in the range 1 ≤ week ≤ maxweek, where maxweek is the week number of the last day of week-year year
2.4.5.9 Durations

A duration consists of a number of seconds.

Since months and seconds are not comparable (a month is not a precise number of seconds, but is instead a period whose exact length depends on the precise day from which it is measured) a duration as defined in this specification cannot include months (or years, which are equivalent to twelve months). Only durations that describe a specific number of seconds can be described.

A string is a valid duration string representing a duration t if it consists of either of the following:

2.4.5.10 Vaguer moments in time

A string is a valid date string with optional time if it is also one of the following:

2.4.6 Colors

A simple color consists of three 8-bit numbers in the range 0..255, representing the red, green, and blue components of the color respectively, in the sRGB color space. [SRGB]

A string is a valid simple color if it is exactly seven characters long, and the first character is a "#" (U+0023) character, and the remaining six characters are all in the range ASCII digits, U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN SMALL LETTER A to U+0066 LATIN SMALL LETTER F, with the first two digits representing the red component, the middle two digits representing the green component, and the last two digits representing the blue component, in hexadecimal.

A string is a valid lowercase simple color if it is a valid simple color and doesn't use any characters in the range U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F.


2.4.7 Space-separated tokens

A set of space-separated tokens is a string containing zero or more words (known as tokens) separated by one or more space characters, where words consist of any string of one or more characters, none of which are space characters.

A string containing a set of space-separated tokens may have leading or trailing space characters.

An unordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated.

An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated but where the order of the tokens is meaningful.

Sets of space-separated tokens sometimes have a defined set of allowed values. When a set of allowed values is defined, the tokens must all be from that list of allowed values; other values are non-conforming. If no such set of allowed values is provided, then all values are conforming.

How tokens in a set of space-separated tokens are to be compared (e.g. case-sensitively or not) is defined on a per-set basis.

2.4.8 Comma-separated tokens

A set of comma-separated tokens is a string containing zero or more tokens each separated from the next by a single "," (U+002C) character, where tokens consist of any string of zero or more characters, neither beginning nor ending with space characters, nor containing any "," (U+002C) characters, and optionally surrounded by space characters.

For instance, the string " a ,b,,d d " consists of four tokens: "a", "b", the empty string, and "d d". Leading and trailing whitespace around each token doesn't count as part of the token, and the empty string can be a token.

Sets of comma-separated tokens sometimes have further restrictions on what consists a valid token. When such restrictions are defined, the tokens must all fit within those restrictions; other values are non-conforming. If no such restrictions are specified, then all values are conforming.

2.4.9 References

A valid hash-name reference to an element of type type is a string consisting of a "#" (U+0023) character followed by a string which exactly matches the value of the name attribute of an element with type type in the document.

2.4.10 Media queries

A string is a valid media query if it matches the media_query_list production of the Media Queries specification. [MQ]

A string matches the environment of the user if it is the empty string, a string consisting of only space characters, or is a media query that matches the user's environment according to the definitions given in the Media Queries specification. [MQ]