GeezerVison

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>

To determine the state of an attribute, use the following steps:

1. If the attribute is not specified:

   1. If the attribute has a missing value default state defined, then return that missing value default state.

   2. Otherwise, return no state.

2. If the attribute's value is an ASCII case-insensitive match for one of the keywords defined for the attribute, then return the state represented by that keyword.

3. If the attribute has an empty value default state defined and the attribute's value is the empty string, then return that empty value default state.

4. If the attribute has an invalid value default state defined, then return that invalid value default state.

5. Return no state.

For reflection purposes, states which have any keywords mapping to them are said to have a canonical keyword. This is determined as follows:

1. If there is only one keyword mapping to the given state, then it is that keyword.

2. If there is only one conforming keyword mapping to the given state, then it is that conforming keyword.

3. If there are two conforming keywords mapping to the given state, and one is the empty string, then the canonical keyword will be the conforming keyword that is not the empty string.

4. Otherwise, the canonical keyword for the state will be explicitly given in the specification for the attribute.

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

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

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

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

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

1. Optionally, a U+002D HYPHEN-MINUS character (-).

2. One or both of the following, in the given order:

   1. A series of one or more ASCII digits.

   2. Both of the following, in the given order:

      1. A single U+002E FULL STOP character (.).

      2. A series of one or more ASCII digits.

3. Optionally:

   1. Either a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E).

   2. Optionally, a U+002D HYPHEN-MINUS character (-) or U+002B PLUS SIGN character (+).

   3. A series of one or more 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 HYPHEN-MINUS 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 HYPHEN-MINUS character (-) between the E and the number and the number is not zero, or else ignoring a U+002B PLUS SIGN character (+) between the E and the number if there is one). If there is no E, then the exponent is treated as zero.

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

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]

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 ASCII digits, representing year, where year > 0
2. A U+002D HYPHEN-MINUS character (-)
3. Two ASCII digits, representing the month month, in the range 1 ≤ month ≤ 12

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 HYPHEN-MINUS character (-)
3. Two ASCII digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and year 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 HYPHEN-MINUS characters (-)
2. Two ASCII digits, representing the month month, in the range 1 ≤ month ≤ 12
3. A U+002D HYPHEN-MINUS character (-)
4. Two ASCII 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.

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

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

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 U+0054 LATIN CAPITAL LETTER T character (T) 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 U+0054 LATIN CAPITAL LETTER T character (T)
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)

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

• A U+005A LATIN CAPITAL LETTER Z character (Z), allowed only if the time zone is UTC

• Or, the following components, in the given order:

  1. Either a U+002B PLUS SIGN character (+) or, if the time-zone offset is not zero, a U+002D HYPHEN-MINUS character (-), representing the sign of the time-zone offset
  2. Two ASCII digits, representing the hours component hour of the time-zone offset, in the range 0 ≤ hour ≤ 23
  3. Optionally, a U+003A COLON character (:)
  4. Two ASCII digits, representing the minutes component minute of the time-zone offset, in the range 0 ≤ minute ≤ 59

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 U+0054 LATIN CAPITAL LETTER T character (T) 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

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:

• Years with fewer than four digits have to be zero-padded. The date "37-12-13" would not be a valid date.
• If the "T" is replaced by a space, it must be a single space character. The string "2001-12-21  12:00Z" (with two spaces between the components) would not be parsed successfully.
• To unambiguously identify a moment in time prior to the introduction of the Gregorian calendar (insofar as moments in time before the formation of UTC can be unambiguously identified), the date has to be first converted to the Gregorian calendar from the calendar in use at the time (e.g. from the Julian calendar). The date of Nero's birth is the 15th of December 37, in the Julian Calendar, which is the 13th of December 37 in the proleptic Gregorian calendar.
• The time and time-zone offset components are not optional.
• Dates before the year one can't be represented as a datetime in this version of HTML.
• Times of specific events in ancient times are, at best, approximations, since time was not well coordinated or measured until relatively recent decades.
• Time-zone offsets differ based on daylight saving time.

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.

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 ASCII digits, representing year, where year > 0
2. A U+002D HYPHEN-MINUS character (-)
3. A U+0057 LATIN CAPITAL LETTER W character (W)
4. Two ASCII 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

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

• A literal U+0050 LATIN CAPITAL LETTER P character followed by one or more of the following subcomponents, in the order given, where the number of days, hours, minutes, and seconds corresponds to the same number of seconds as in t:

  1. One or more ASCII digits followed by a U+0044 LATIN CAPITAL LETTER D character, representing a number of days.

  2. A U+0054 LATIN CAPITAL LETTER T character followed by one or more of the following subcomponents, in the order given:

     1. One or more ASCII digits followed by a U+0048 LATIN CAPITAL LETTER H character, representing a number of hours.

     2. One or more ASCII digits followed by a U+004D LATIN CAPITAL LETTER M character, representing a number of minutes.

     3. The following components:

        1. One or more ASCII digits, representing a number of seconds.

        2. Optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.

        3. A U+0053 LATIN CAPITAL LETTER S character.

  This, as with a number of other date- and time-related microsyntaxes defined in this specification, is based on one of the formats defined in ISO 8601. [ISO8601]

• One or more duration time components, each with a different duration time component scale, in any order; the sum of the represented seconds being equal to the number of seconds in t.

  A duration time component is a string consisting of the following components:

  1. Zero or more ASCII whitespace.

  2. One or more ASCII digits, representing a number of time units, scaled by the duration time component scale specified (see below) to represent a number of seconds.

  3. If the duration time component scale specified is 1 (i.e. the units are seconds), then, optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.

  4. Zero or more ASCII whitespace.

  5. One of the following characters, representing the duration time component scale of the time unit used in the numeric part of the duration time component:

     U+0057 LATIN CAPITAL LETTER W character

     U+0077 LATIN SMALL LETTER W character

     Weeks. The scale is 604800.

     U+0044 LATIN CAPITAL LETTER D character

     U+0064 LATIN SMALL LETTER D character

     Days. The scale is 86400.

     U+0048 LATIN CAPITAL LETTER H character

     U+0068 LATIN SMALL LETTER H character

     Hours. The scale is 3600.

     U+004D LATIN CAPITAL LETTER M character

     U+006D LATIN SMALL LETTER M character

     Minutes. The scale is 60.

     U+0053 LATIN CAPITAL LETTER S character

     U+0073 LATIN SMALL LETTER S character

     Seconds. The scale is 1.

  6. Zero or more ASCII whitespace.

  This is not based on any of the formats in ISO 8601. It is intended to be a more human-readable alternative to the ISO 8601 duration format.

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

• A valid date string
• A valid global date and time string

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

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

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.

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

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

A string is a valid media query list if it matches the <media-query-list> production of Media Queries. [MQ]

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

To create a new unique internal value, return a unique internal value that has never previously been returned by this algorithm.