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属性の状態を判別するには、次のステップを利用する：

1. 属性が指定されていない場合：

   1. 属性が欠損値のデフォルト状態が定義されている場合、その欠落値のデフォルト状態を返す。

   2. そうでなければ、状態なしを返す。

2. 属性の値が、属性に定義されているキーワードの1つとASCII大文字・小文字不区別でマッチする場合、そのキーワードで表される状態を返す。

3. 属性が空の値のデフォルト状態が定義されており、その属性の値が空の文字列である場合、その空の値のデフォルト状態を返す。

4. 属性が無効値のデフォルト状態が定義されている場合、その無効値のデフォルト状態を返す。

5. 状態なしを返す。

反射の目的で、マッピングされているキーワードがある状態は、正規のキーワードを持つと言われる。これは次のように決定される：

1. 特定の状態にマッピングされているキーワードが1つしかない場合、そのキーワードである。

2. 特定の状態にマッピングされている適合キーワードが1つしかない場合、それはその適合キーワードである。

3. 指定された状態にマッピングする2つの適合キーワードがあり、1つが空文字列である場合、正規キーワードは空の文字列ではない適合キーワードになる。

4. そうでなければ、状態の正規キーワードは、属性の仕様で明示的に指定される。

文字列が1つ以上のASCII 数字、任意で接頭辞U+002D HYPHEN-MINUS文字（-）を持つ場合、文字列は妥当な整数である。

接頭辞U+002D HYPHEN-MINUS（-）接頭辞なしの妥当な整数は、10進数を表す。U+002D HYPHEN-MINUS文字（-）接頭辞ありの妥当な整数は、U+002D HYPHEN-MINUSに続く10進数を表し、0から減算される。

The rules for parsing integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either an integer or an error.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let sign have the value "positive".

4. Skip ASCII whitespace within input given position.

5. If position is past the end of input, return an error.

6. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS character (-):

   1. Let sign be "negative".
   2. Advance position to the next character.
   3. If position is past the end of input, return an error.

   Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):

   1. Advance position to the next character. (The "+" is ignored, but it is not conforming.)
   2. If position is past the end of input, return an error.

7. If the character indicated by position is not an ASCII digit, then return an error.

8. Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Let value be that integer.

9. If sign is "positive", return value, otherwise return the result of subtracting value from zero.

1つ以上のASCII数字からなる場合、文字列は妥当な非負整数である。

妥当な非負整数は、10進数である数を表す。

The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either zero, a positive integer, or an error.

1. Let input be the string being parsed.

2. Let value be the result of parsing input using the rules for parsing integers.

3. If value is an error, return an error.

4. If value is less than zero, return an error.

5. Return value.

次の場合、文字列は妥当な浮動小数点数である：

1. 任意で、1つのA U+002D HYPHEN-MINUS文字（-）。

2. 次のいずれかまたは両方の、与えられた順：

   1. ひと続きの1つ以上のASCII数字。

   2. 次の両方の、与えられた順で：

      1. 1つのU+002E FULL STOP文字（.）。

      2. ひと続きの1つ以上のASCII数字。

3. 任意で：

   1. 1つの U+0065 LATIN SMALL LETTER E文字（e）か1つのU+0045 LATIN CAPITAL LETTER E文字（E）のいずれか。

   2. 任意で、1つのU+002D HYPHEN-MINUS文字（-）または1つのU+002B PLUS SIGN文字（+）。

   3. ひと続きの1つ以上のASCII数字。

妥当な浮動小数点数は、10の累乗による仮数部の乗算によって得られる。ここで乗算は最初の数であり、10進数として解釈される（もしあれば、小数点および小数点の後の数を含み、文字列全体がU+002D HYPHEN-MINUS文字（-）で始まるおよび数値が0でない場合、負数として仮数部を解釈する）。またここで、もしあれば、指数はEの後の数字である（Eと数字と数字の間にU+002D HYPHEN-MINUS文字（-）がある場合、負数として解釈され、数字が0でない、またはその他Eと数字の間にU+002B PLUS SIGN文字（+）が存在する場合無視できる）。Eが存在しない場合、指数は0として扱われる。

The best representation of the number n as a floating-point number is the string obtained from running ToString(n). The abstract operation ToString is not uniquely determined. When there are multiple possible strings that could be obtained from ToString for a particular value, the user agent must always return the same string for that value (though it may differ from the value used by other user agents).

The rules for parsing floating-point number values are as given in the following algorithm. This algorithm must be aborted at the first step that returns something. This algorithm will return either a number or an error.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let value have the value 1.

4. Let divisor have the value 1.

5. Let exponent have the value 1.

6. Skip ASCII whitespace within input given position.

7. If position is past the end of input, return an error.

8. If the character indicated by position is a U+002D HYPHEN-MINUS character (-):

   1. Change value and divisor to −1.
   2. Advance position to the next character.
   3. If position is past the end of input, return an error.

   Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):

   1. Advance position to the next character. (The "+" is ignored, but it is not conforming.)
   2. If position is past the end of input, return an error.

9. If the character indicated by position is a U+002E FULL STOP (.), and that is not the last character in input, and the character after the character indicated by position is an ASCII digit, then set value to zero and jump to the step labeled fraction.

10. If the character indicated by position is not an ASCII digit, then return an error.

11. Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Multiply value by that integer.

12. If position is past the end of input, jump to the step labeled conversion.

13. Fraction: If the character indicated by position is a U+002E FULL STOP (.), run these substeps:

    1. Advance position to the next character.

    2. If position is past the end of input, or if the character indicated by position is not an ASCII digit, U+0065 LATIN SMALL LETTER E (e), or U+0045 LATIN CAPITAL LETTER E (E), then jump to the step labeled conversion.

    3. If the character indicated by position is a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E), skip the remainder of these substeps.

    4. Fraction loop: Multiply divisor by ten.

    5. Add the value of the character indicated by position, interpreted as a base-ten digit (0..9) and divided by divisor, to value.

    6. Advance position to the next character.

    7. If position is past the end of input, then jump to the step labeled conversion.

    8. If the character indicated by position is an ASCII digit, jump back to the step labeled fraction loop in these substeps.

14. If the character indicated by position is U+0065 (e) or a U+0045 (E):

    1. Advance position to the next character.

    2. If position is past the end of input, then jump to the step labeled conversion.

    3. If the character indicated by position is a U+002D HYPHEN-MINUS character (-):

       1. Change exponent to −1.
       2. Advance position to the next character.

       3. If position is past the end of input, then jump to the step labeled conversion.

       Otherwise, if the character indicated by position is a U+002B PLUS SIGN character (+):

       1. Advance position to the next character.

       2. If position is past the end of input, then jump to the step labeled conversion.

    4. If the character indicated by position is not an ASCII digit, then jump to the step labeled conversion.

    5. Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Multiply exponent by that integer.

    6. Multiply value by ten raised to the exponentth power.

15. Conversion: Let S be the set of finite IEEE 754 double-precision floating-point values except −0, but with two special values added: 2¹⁰²⁴ and −2¹⁰²⁴.

16. Let rounded-value be the number in S that is closest to value, selecting the number with an even significand if there are two equally close values. (The two special values 2¹⁰²⁴ and −2¹⁰²⁴ are considered to have even significands for this purpose.)

17. If rounded-value is 2¹⁰²⁴ or −2¹⁰²⁴, return an error.

18. Return rounded-value.

The rules for parsing dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than or equal to 0.0, or failure; if a number is returned, then it is further categorized as either a percentage or a length.

1. Let input be the string being parsed.

2. Let position be a position variable for input, initially pointing at the start of input.

3. Skip ASCII whitespace within input given position.

4. If position is past the end of input or the code point at position within input is not an ASCII digit, then return failure.

5. Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Let value be that number.

6. If position is past the end of input, then return value as a length.

7. If the code point at position within input is U+002E (.):

   1. Advance position by 1.

   2. If position is past the end of input or the code point at position within input is not an ASCII digit, then return the current dimension value with value, input, and position.

   3. Let divisor have the value 1.

   4. While true:

      1. Multiply divisor by ten.

      2. Add the value of the code point at position within input, interpreted as a base-ten digit (0..9) and divided by divisor, to value.

      3. Advance position by 1.

      4. If position is past the end of input, then return value as a length.

      5. If the code point at position within input is not an ASCII digit, then break.

8. Return the current dimension value with value, input, and position.

The current dimension value, given value, input, and position, is determined as follows:

1. If position is past the end of input, then return value as a length.

2. If the code point at position within input is U+0025 (%), then return value as a percentage.

3. Return value as a length.

The rules for parsing nonzero dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than 0.0, or an error; if a number is returned, then it is further categorized as either a percentage or a length.

1. Let input be the string being parsed.

2. Let value be the result of parsing input using the rules for parsing dimension values.

3. If value is an error, return an error.

4. If value is zero, return an error.

5. If value is a percentage, return value as a percentage.

6. Return value as a length.

妥当な浮動小数点数リストは、U+002C COMMA文字によって区切られる多数の妥当な浮動小数点数であり、他の文字を持たない（たとえばASCII空白文字のない）。さらに、与えられる浮動小数点数の数、または許可される値の範囲には制限があるかもしれない。

The rules for parsing a list of floating-point numbers are as follows:

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let numbers be an initially empty list of floating-point numbers. This list will be the result of this algorithm.

4. Collect a sequence of code points that are ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position. This skips past any leading delimiters.

5. While position is not past the end of input:

   1. Collect a sequence of code points that are not ASCII whitespace, U+002C COMMA, U+003B SEMICOLON, ASCII digits, U+002E FULL STOP, or U+002D HYPHEN-MINUS characters from input given position. This skips past leading garbage.

   2. Collect a sequence of code points that are not ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position, and let unparsed number be the result.

   3. Let number be the result of parsing unparsed number using the rules for parsing floating-point number values.

   4. If number is an error, set number to zero.

   5. Append number to numbers.

   6. Collect a sequence of code points that are ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position. This skips past the delimiter.

6. Return numbers.

The rules for parsing a list of dimensions are as follows. These rules return a list of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.

1. Let raw input be the string being parsed.

2. If the last character in raw input is a U+002C COMMA character (,), then remove that character from raw input.

3. Split the string raw input on commas. Let raw tokens be the resulting list of tokens.

4. Let result be an empty list of number/unit pairs.

5. For each token in raw tokens, run the following substeps:

   1. Let input be the token.

   2. Let position be a pointer into input, initially pointing at the start of the string.

   3. Let value be the number 0.

   4. Let unit be absolute.

   5. If position is past the end of input, set unit to relative and jump to the last substep.

   6. If the character at position is an ASCII digit, collect a sequence of code points that are ASCII digits from input given position, interpret the resulting sequence as an integer in base ten, and increment value by that integer.

   7. If the character at position is U+002E (.):

      1. Collect a sequence of code points consisting of ASCII whitespace and ASCII digits from input given position. Let s be the resulting sequence.

      2. Remove all ASCII whitespace in s.

      3. If s is not the empty string:

         1. Let length be the number of characters in s (after the spaces were removed).

         2. Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10^length.

         3. Increment value by fraction.

   8. Skip ASCII whitespace within input given position.

   9. If the character at position is a U+0025 PERCENT SIGN character (%), then set unit to percentage.

      Otherwise, if the character at position is a U+002A ASTERISK character (*), then set unit to relative.

   10. Add an entry to result consisting of the number given by value and the unit given by unit.

6. Return the list result.

下記のアルゴリズムにおいて、年yearの月monthの日数は：monthが1、3、5、7、8、10、12ならば31である。monthが4、6、9、11ならば30である。monthが2かつyearが400で割り切れる数、またはyearが4で割り切れるが100で割り切れないならば29であり、そうでなければ28である。これは、グレゴリオ暦の閏年を考慮に入れている。[GREGORIAN]

与えられた順で次のコンポーネントからなる場合、文字列は、年yearおよび月monthで表される妥当な月文字列である：

1. 4桁以上で表されるyear。ここでyear > 0である。
2. A U+002D HYPHEN-MINUS文字（-）
3. 1 ≤ month ≤ 12の範囲で、月monthを表す2つのASCII数字

The rules to parse a month string are as follows. This will return either a year and month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a month component to obtain year and month. If this returns nothing, then fail.

4. If position is not beyond the end of input, then fail.

5. Return year and month.

The rules to parse a month component, given an input string and a position, are as follows. This will return either a year and a month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let year be that number.

2. If year is not a number greater than zero, then fail.

3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let month be that number.

5. If month is not a number in the range 1 ≤ month ≤ 12, then fail.

6. Return year and month.

与えられた順で次のコンポーネントからなる場合、文字列は年year、月month、日dayで表される妥当な日付文字列である：

1. yearおよびmonthで表される、妥当な月文字列
2. A U+002D HYPHEN-MINUS文字（-）
3. 1 ≤ day ≤ maxdayの範囲でのdayで表される2つのASCII数字。ここでmaxdayは年yearおよび月monthでの日の数である。

The rules to parse a date string are as follows. This will return either a date, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

4. If position is not beyond the end of input, then fail.

5. Let date be the date with year year, month month, and day day.

6. Return date.

The rules to parse a date component, given an input string and a position, are as follows. This will return either a year, a month, and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Parse a month component to obtain year and month. If this returns nothing, then fail.

2. Let maxday be the number of days in month month of year year.

3. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let day be that number.

5. If day is not a number in the range 1 ≤ day ≤ maxday, then fail.

6. Return year, month, and day.

与えられた順で次のコンポーネントからなる場合、文字列は月monthおよび日dayで表される妥当な年なし日付文字列である：

1. 任意で、2つのA U+002D HYPHEN-MINUS文字（-）
2. 1 ≤ month ≤ 12の範囲で、月monthを表す2つのASCII数字
3. A U+002D HYPHEN-MINUS文字（-）
4. 1 ≤ day ≤ maxdayの範囲でのdayで表される2つのASCII数字。ここでmaxdayは月monthかつ任意の閏年（たとえば4または2000）における日数である。

言い換えると、2月を意味するmonthが"02"である場合、あたかもその年は閏年かのように、日は29であってもよい。

The rules to parse a yearless date string are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a yearless date component to obtain month and day. If this returns nothing, then fail.

4. If position is not beyond the end of input, then fail.

5. Return month and day.

The rules to parse a yearless date component, given an input string and a position, are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Collect a sequence of code points that are U+002D HYPHEN-MINUS characters (-) from input given position. If the collected sequence is not exactly zero or two characters long, then fail.

2. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let month be that number.

3. If month is not a number in the range 1 ≤ month ≤ 12, then fail.

4. Let maxday be the number of days in month month of any arbitrary leap year (e.g. 4 or 2000).

5. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

6. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let day be that number.

7. If day is not a number in the range 1 ≤ day ≤ maxday, then fail.

8. Return month and day.

与えられた順で次のコンポーネントからなる場合、文字列は、時hour、分minute、秒secondで表される妥当な時刻文字列である：

1. 0 ≤ hour ≤ 23の範囲で、hourを表す2つのASCII数字
2. A U+003A COLON文字（:）
3. 0 ≤ minute ≤ 59の範囲でminuteを表す2つのASCII数字
4. If second is nonzero, or optionally if second is zero:
   1. A U+003A COLON文字（:）
   2. 0 ≤ s ≤ 59の範囲で、second整数部を表す2つのASCII数字
   3. secondが非整数である場合、または任意でsecondが整数である場合：
      1. A U+002E FULL STOP character (.)
      2. second分数部で表される、1、2、また3桁

secondコンポーネントは60または61にはなり得ない。閏秒を表すことはできない。

The rules to parse a time string are as follows. This will return either a time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

4. If position is not beyond the end of input, then fail.

5. Let time be the time with hour hour, minute minute, and second second.

6. Return time.

The rules to parse a time component, given an input string and a position, are as follows. This will return either an hour, a minute, and a second, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let hour be that number.

2. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.

3. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

4. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let minute be that number.

5. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.

6. Let second be 0.

7. If position is not beyond the end of input and the character at position is U+003A (:):

   1. Advance position to the next character in input.

   2. If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not both ASCII digits, then fail.

   3. Collect a sequence of code points that are either ASCII digits or U+002E FULL STOP characters from input given position. If the collected sequence is three characters long, or if it is longer than three characters long and the third character is not a U+002E FULL STOP character, or if it has more than one U+002E FULL STOP character, then fail. Otherwise, interpret the resulting sequence as a base-ten number (possibly with a fractional part). Set second to that number.

   4. If second is not a number in the range 0 ≤ second < 60, then fail.

8. Return hour, minute, and second.

与えられた順で次のコンポーネントからなる場合、文字列は妥当なローカル日付および時刻文字列である：

1. 日付を表す妥当な日付文字列
2. U+0054 LATIN CAPITAL LETTER T文字（T）またはU+0020 SPACE文字
3. 時刻を表す妥当な時刻文字列

与えられた順で次のコンポーネントからなる場合、文字列は妥当な規格化ローカル日付および時刻文字列である：

1. 日付を表す妥当な日付文字列
2. A U+0054 LATIN CAPITAL LETTER T文字（T）
3. 時刻を表す妥当な時刻文字列は、与えられた時刻に対して可能な限り最短の文字列として表現される（たとえば、与えられた時刻がその分の0秒である場合、完全に秒のコンポーネントを省略する）

The rules to parse a local date and time string are as follows. This will return either a date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

4. If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.

5. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

6. If position is not beyond the end of input, then fail.

7. Let date be the date with year year, month month, and day day.

8. Let time be the time with hour hour, minute minute, and second second.

9. Return date and time.

次のいずれかからなる場合、文字列は、タイムゾーンオフセットを表す妥当なタイムゾーンオフセット文字列である：

• タイムゾーンがUTCの場合のみ許される、U+005A LATIN CAPITAL LETTER Z文字（Z）

• または、与えられた順で次のコンポーネント：

  1. タイムゾーンオフセットの符号を表す、U+002B PLUS SIGN文字（+）、またはタイムゾーンオフセットが0でない場合のU+002D HYPHEN-MINUS文字（-）のいずれか
  2. 0 ≤ hour ≤ 23の範囲で、タイムゾーンオフセットの時コンポーネントhourを表す2つのASCII数字
  3. 任意で、A U+003A COLON文字（:）
  4. 0 ≤ minute ≤ 59の範囲で、タイムゾーンオフセットの分コンポーネントminuteを表す2つのASCII数字

The rules to parse a time-zone offset string are as follows. This will return either a time-zone offset, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a time-zone offset component to obtain timezone_hours and timezone_minutes. If this returns nothing, then fail.

4. If position is not beyond the end of input, then fail.

5. Return the time-zone offset that is timezone_hours hours and timezone_minutes minutes from UTC.

The rules to parse a time-zone offset component, given an input string and a position, are as follows. This will return either time-zone hours and time-zone minutes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. If the character at position is a U+005A LATIN CAPITAL LETTER Z character (Z):

   1. Let timezone_hours be 0.

   2. Let timezone_minutes be 0.

   3. Advance position to the next character in input.

   Otherwise, if the character at position is either a U+002B PLUS SIGN (+) or a U+002D HYPHEN-MINUS (-):

   1. If the character at position is a U+002B PLUS SIGN (+), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS (-); let sign be "negative".

   2. Advance position to the next character in input.

   3. Collect a sequence of code points that are ASCII digits from input given position. Let s be the collected sequence.

   4. If s is exactly two characters long:

      1. Interpret s as a base-ten integer. Let timezone_hours be that number.

      2. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

      3. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let timezone_minutes be that number.

      If s is exactly four characters long:

      1. Interpret the first two characters of s as a base-ten integer. Let timezone_hours be that number.

      2. Interpret the last two characters of s as a base-ten integer. Let timezone_minutes be that number.

      Otherwise, fail.

   5. If timezone_hours is not a number in the range 0 ≤ timezone_hours ≤ 23, then fail.
   6. If sign is "negative", then negate timezone_hours.
   7. If timezone_minutes is not a number in the range 0 ≤ timezone_minutes ≤ 59, then fail.
   8. If sign is "negative", then negate timezone_minutes.

   Otherwise, fail.

2. Return timezone_hours and timezone_minutes.

与えられた順で次のコンポーネントからなる場合、日付、時刻、タイムゾーンオフセットを表す文字列は妥当なグローバル日付および時刻である：

1. 日付を表す妥当な日付文字列
2. U+0054 LATIN CAPITAL LETTER T文字（T）またはU+0020 SPACE文字
3. 時刻を表す妥当な時刻文字列
4. タイムゾーンオフセットを表す妥当なタイムゾーンオフセット文字列

The rules to parse a global date and time string are as follows. This will return either a time in UTC, with associated time-zone offset information for roundtripping or display purposes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Parse a date component to obtain year, month, and day. If this returns nothing, then fail.

4. If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.

5. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

6. If position is beyond the end of input, then fail.

7. Parse a time-zone offset component to obtain timezone_hours and timezone_minutes. If this returns nothing, then fail.

8. If position is not beyond the end of input, then fail.

9. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezone_hours hours and timezone_minutes minutes. That moment in time is a moment in the UTC time zone.

10. Let timezone be timezone_hours hours and timezone_minutes minutes from UTC.

11. Return time and timezone.

最初の日（1月1日）が木曜である先発グレコリオ暦の年year、または最初の日（1月1日）が木曜である先発グレコリオ暦の年yearのいずれかに対応する場合、数字yearとともに週番号年は53週を持つ。ここで、yearは400で割り切れる数字、または4で割り切れるが100で割り切れない数字である。他のすべての週番号年は52週である。

53週をもつ週番号年の最終日の週番号は53であり、52週をもつ週番号年の最終日の週番号は52である。

与えられた順で次のコンポーネントからなる場合、文字列は、週番号年yearおよび週weekを表す妥当な週文字列である：

1. 4桁以上で表されるyear。ここでyear > 0である。
2. A U+002D HYPHEN-MINUS文字（-）
3. U+0057 LATIN CAPITAL LETTER W文字（W）
4. 1 ≤ week ≤ maxweekの範囲で、週weekを表す2つのASCII数字。ここで maxweekは週番号年yearの最終日の週番号である。

The rules to parse a week string are as follows. This will return either a week-year number and week number, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let year be that number.

4. If year is not a number greater than zero, then fail.

5. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

6. If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character (W), then fail. Otherwise, move position forwards one character.

7. Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let week be that number.

8. Let maxweek be the week number of the last day of year year.

9. If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.

10. If position is not beyond the end of input, then fail.

11. Return the week-year number year and the week number week.

次のいずれかからなる場合、文字列は、継続時間tで表す妥当な継続時間文字列である：

• 与えられた順でリテラルにU+0050 LATIN CAPITAL LETTER P文字の後に次のサブコンポーネントが続く。ここで日、時、分および秒数はtとして同じ秒数に対応する：

  1. U+0044 LATIN CAPITAL LETTER D文字の後に続く、日数を表す1つ以上のASCII数字。

  2. 与えられた順で、U+0054 LATIN CAPITAL LETTER T文字の後に次のサブコンポーネントが続く：

     1. U+0048 LATIN CAPITAL LETTER H文字の後に続く、時数を表す1つ以上のASCII数字。

     2. U+0044 LATIN CAPITAL LETTER M文字の後に続く、分数を表す1つ以上のASCII数字。

     3. 次のコンポーネント：

        1. 秒数を表す、1つ以上のASCII数字。

        2. 任意で、秒以下を表すU+002E FULL STOP文字（.）の後に続く1、2、または3つのASCII数字。

        3. U+0053 LATIN CAPITAL LETTER S文字。

  これは、この仕様で定義される他の日付および時刻依存のマイクロ構文と同様に、ISO 8601で定義される形式の1つに基づく。[ISO8601]

• 任意の順で、それぞれ異なる継続時間コンポーネントのスケールを伴う、1つ以上の継続時間コンポーネント。秒数tと等価である秒数で表される合計。

  継続時間コンポーネントは次のコンポーネントからなる文字列である：

  1. 0個以上のASCII空白文字。

  2. 秒数を表現するために指定された継続時間コンポーネントスケール（下記参照）でスケールされる時刻単位数で表す、1つ以上のASCII数字。

  3. 指定された継続時間コンポーネントスケールが1（すなわち単位が秒）の場合、任意で、U+002E FULL STOP文字（.）文字の後に続く秒以下を表す1、2、または3つのASCII数字。

  4. 0個以上のASCII空白文字。

  5. 継続時間コンポーネントの数字部で用いられる時刻単位の継続時間コンポーネントスケールを表す、次の文字の1つ：

     U+0057 LATIN CAPITAL LETTER W文字

     U+0077 LATIN SMALL LETTER W文字

     週スケールは604800である。

     U+0044 LATIN CAPITAL LETTER D文字

     U+0064 LATIN SMALL LETTER D文字

     日。スケールは86400である。

     U+0048 LATIN CAPITAL LETTER H文字

     U+0068 LATIN SMALL LETTER H文字

     時。スケールは3600である。

     U+004D LATIN CAPITAL LETTER M文字

     U+006D LATIN SMALL LETTER M文字

     分。スケールは60である。

     U+0053 LATIN CAPITAL LETTER S文字

     U+0073 LATIN SMALL LETTER S文字

     秒。スケールは1である。

  6. 0個以上のASCII空白文字。

  これはISO 8601での形式のいずれにも基づかない。ISO 8601継続時間形式の代わりに、より人間に読みやすくすることを意図する。

The rules to parse a duration string are as follows. This will return either a duration or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let months, seconds, and component count all be zero.

4. Let M-disambiguator be minutes.

   This flag's other value is months. It is used to disambiguate the "M" unit in ISO8601 durations, which use the same unit for months and minutes. Months are not allowed, but are parsed for future compatibility and to avoid misinterpreting ISO8601 durations that would be valid in other contexts.

5. Skip ASCII whitespace within input given position.

6. If position is past the end of input, then fail.

7. If the character in input pointed to by position is a U+0050 LATIN CAPITAL LETTER P character, then advance position to the next character, set M-disambiguator to months, and skip ASCII whitespace within input given position.

8. While true:

   1. Let units be undefined. It will be assigned one of the following values: years, months, weeks, days, hours, minutes, and seconds.

   2. Let next character be undefined. It is used to process characters from the input.

   3. If position is past the end of input, then break.

   4. If the character in input pointed to by position is a U+0054 LATIN CAPITAL LETTER T character, then advance position to the next character, set M-disambiguator to minutes, skip ASCII whitespace within input given position, and continue.

   5. Set next character to the character in input pointed to by position.

   6. If next character is a U+002E FULL STOP character (.), then let N be 0. (Do not advance position. That is taken care of below.)

      Otherwise, if next character is an ASCII digit, then collect a sequence of code points that are ASCII digits from input given position, interpret the resulting sequence as a base-ten integer, and let N be that number.

      Otherwise, next character is not part of a number; fail.

   7. If position is past the end of input, then fail.

   8. Set next character to the character in input pointed to by position, and this time advance position to the next character. (If next character was a U+002E FULL STOP character (.) before, it will still be that character this time.)

   9. If next character is U+002E (.):

      1. Collect a sequence of code points that are ASCII digits from input given position. Let s be the resulting sequence.

      2. If s is the empty string, then fail.

      3. Let length be the number of characters in s.

      4. Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10^length.

      5. Increment N by fraction.

      6. Skip ASCII whitespace within input given position.

      7. If position is past the end of input, then fail.

      8. Set next character to the character in input pointed to by position, and advance position to the next character.

      9. If next character is neither a U+0053 LATIN CAPITAL LETTER S character nor a U+0073 LATIN SMALL LETTER S character, then fail.

      10. Set units to seconds.

      Otherwise:

      1. If next character is ASCII whitespace, then skip ASCII whitespace within input given position, set next character to the character in input pointed to by position, and advance position to the next character.

      2. If next character is a U+0059 LATIN CAPITAL LETTER Y character, or a U+0079 LATIN SMALL LETTER Y character, set units to years and set M-disambiguator to months.

         If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is months, then set units to months.

         If next character is a U+0057 LATIN CAPITAL LETTER W character or a U+0077 LATIN SMALL LETTER W character, set units to weeks and set M-disambiguator to minutes.

         If next character is a U+0044 LATIN CAPITAL LETTER D character or a U+0064 LATIN SMALL LETTER D character, set units to days and set M-disambiguator to minutes.

         If next character is a U+0048 LATIN CAPITAL LETTER H character or a U+0068 LATIN SMALL LETTER H character, set units to hours and set M-disambiguator to minutes.

         If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is minutes, then set units to minutes.

         If next character is a U+0053 LATIN CAPITAL LETTER S character or a U+0073 LATIN SMALL LETTER S character, set units to seconds and set M-disambiguator to minutes.

         Otherwise, if next character is none of the above characters, then fail.

   10. Increment component count.

   11. Let multiplier be 1.

   12. If units is years, multiply multiplier by 12 and set units to months.

   13. If units is months, add the product of N and multiplier to months.

       Otherwise:

       1. If units is weeks, multiply multiplier by 7 and set units to days.

       2. If units is days, multiply multiplier by 24 and set units to hours.

       3. If units is hours, multiply multiplier by 60 and set units to minutes.

       4. If units is minutes, multiply multiplier by 60 and set units to seconds.

       5. Forcibly, units is now seconds. Add the product of N and multiplier to seconds.

   14. Skip ASCII whitespace within input given position.

9. If component count is zero, fail.

10. If months is not zero, fail.

11. Return the duration consisting of seconds seconds.

次のいずれかである場合、文字列は任意の時刻を持つ妥当な日付文字列である：

• 妥当な日付文字列
• 妥当なグローバル日付および時刻文字列

The rules to parse a date or time string are as follows. The algorithm will return either a date, a time, a global date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Set start position to the same position as position.

4. Set the date present and time present flags to true.

5. Parse a date component to obtain year, month, and day. If this fails, then set the date present flag to false.

6. If date present is true, and position is not beyond the end of input, and the character at position is either a U+0054 LATIN CAPITAL LETTER T character (T) or a U+0020 SPACE character, then advance position to the next character in input.

   Otherwise, if date present is true, and either position is beyond the end of input or the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then set time present to false.

   Otherwise, if date present is false, set position back to the same position as start position.

7. If the time present flag is true, then parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.

8. If the date present and time present flags are both true, but position is beyond the end of input, then fail.

9. If the date present and time present flags are both true, parse a time-zone offset component to obtain timezone_hours and timezone_minutes. If this returns nothing, then fail.

10. If position is not beyond the end of input, then fail.

11. If the date present flag is true and the time present flag is false, then let date be the date with year year, month month, and day day, and return date.

    Otherwise, if the time present flag is true and the date present flag is false, then let time be the time with hour hour, minute minute, and second second, and return time.

    Otherwise, let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezone_hours hours and timezone_minutes minutes, that moment in time being a moment in the UTC time zone; let timezone be timezone_hours hours and timezone_minutes minutes from UTC; and return time and timezone.

Some obsolete legacy attributes parse colors using the rules for parsing a legacy color value, given a string input. They will return either a CSS color or failure.

1. If input is the empty string, then return failure.

2. Strip leading and trailing ASCII whitespace from input.

3. If input is an ASCII case-insensitive match for "transparent", then return failure.

4. If input is an ASCII case-insensitive match for one of the named colors, then return the CSS color corresponding to that keyword. [CSSCOLOR]

   CSS2 System Colors are not recognized.

5. If input's code point length is four, and the first character in input is U+0023 (#), and the last three characters of input are all ASCII hex digits:

   1. Let result be a CSS color.

   2. Interpret the second character of input as a hexadecimal digit; let the red component of result be the resulting number multiplied by 17.

   3. Interpret the third character of input as a hexadecimal digit; let the green component of result be the resulting number multiplied by 17.

   4. Interpret the fourth character of input as a hexadecimal digit; let the blue component of result be the resulting number multiplied by 17.

   5. Return result.

6. Replace any code points greater than U+FFFF in input (i.e., any characters that are not in the basic multilingual plane) with "00".

7. If input's code point length is greater than 128, truncate input, leaving only the first 128 characters.

8. If the first character in input is U+0023 (#), then remove it.

9. Replace any character in input that is not an ASCII hex digit with U+0030 (0).

10. While input's code point length is zero or not a multiple of three, append U+0030 (0) to input.

11. Split input into three strings of equal code point length, to obtain three components. Let length be the code point length that all of those components have (one third the code point length of input).

12. If length is greater than 8, then remove the leading length-8 characters in each component, and let length be 8.

13. While length is greater than two and the first character in each component is U+0030 (0), remove that character and reduce length by one.

14. If length is still greater than two, truncate each component, leaving only the first two characters in each.

15. Let result be a CSS color.

16. Interpret the first component as a hexadecimal number; let the red component of result be the resulting number.

17. Interpret the second component as a hexadecimal number; let the green component of result be the resulting number.

18. Interpret the third component as a hexadecimal number; let the blue component of result be the resulting number.

19. Return result.

空白区切りトークンの集合は、1つ以上のASCII空白文字によって区切られた0個以上の単語（トークンとして知られる）を含む文字列である。ここで、単語は1つ以上の文字を含み、ASCII空白文字を含まない。

空白区切りトークンの集合を構成する文字列は、先頭または末尾にASCII空白文字を持ってもよい。

順不同の一意な空白区切りトークンの集合は、繰り返しトークンのない空白区切りトークンの集合である。

順序付きの一意な空白区切りトークンの集合は、繰り返しトークンはないが、トークンの順序が意味のある空白区切りトークンの集合である。

コンマ区切りトークンの集合は、それぞれ単一のU+002C COMMA文字（,）で区切られる0個以上のトークンを含む文字列である。ここでトークンは0個以上の任意の文字列からなり、先頭も末尾もASCII空白文字でなく、U+002C COMMA文字（,）を含まず、任意でASCII空白文字に囲まれるものである。

タイプtype要素の妥当なハッシュ名参照は、 U+0023 NUMBER SIGN文字（#）の後に同じツリーでタイプtypeをもつ要素のname属性の値に正確に一致する文字列から構成される文字列である。

The rules for parsing a hash-name reference to an element of type type, given a context node scope, are as follows:

1. If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null.

2. Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.

3. Return the first element of type type in scope's tree, in tree order, that has an id or name attribute whose value is s, or null if there is no such element.

   Although id attributes are accounted for when parsing, they are not used in determining whether a value is a valid hash-name reference. That is, a hash-name reference that refers to an element based on id is a conformance error (unless that element also has a name attribute with the same value).

Media Queriesの<media-query-list>生成物に一致する場合、文字列は妥当なメディアクエリーリストである。[MQ]

空文字列、ASCII空白文字のみからなる文字列、またはMedia Queriesで与えられる定義に従ったユーザー環境にマッチするメディアクエリーの場合、文字列はユーザー環境に一致する。[MQ]

新しい一意の内部値を作成するには、このアルゴリズムによって以前に返されたことのない一意の内部値を返す。