This specification refers to both HTML and XML attributes and DOM attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and DOM attributes for those from the DOM. Similarly, the term "properties" is used for both ECMAScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.
The term HTML documents is sometimes used in contrast with XML documents to specifically mean documents that were parsed using an HTML parser (as opposed to using an XML parser or created purely through the DOM).
Generally, when the specification states that a feature applies to HTML or XHTML, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XHTML)".
This specification uses the term document to refer to any use of HTML, ranging from short static documents to long essays or reports with rich multimedia, as well as to fully-fledged interactive applications.
For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.
Some of the algorithms in this specification, for historical reasons, require the user agent to pause until some condition has been met. While a user agent is paused, it must ensure that no scripts execute (e.g. no event handlers, no timers, etc). User agents should remain responsive to user input while paused, however, albeit without letting the user interact with Web pages where that would involve invoking any script.
To ease migration from HTML to XHTML, UAs
conforming to this specification will place elements in HTML in the
http://www.w3.org/1999/xhtml namespace, at least for
the purposes of the DOM and CSS. The term "elements in the HTML
namespace", or "HTML elements" for short, when used
in this specification, thus refers to both HTML and XHTML
elements.
Unless otherwise stated, all elements defined or mentioned in
this specification are in the
http://www.w3.org/1999/xhtml namespace, and all
attributes defined or mentioned in this specification have no
namespace (they are in the per-element partition).
When an XML name, such as an attribute or element name, is
referred to in the form prefix:localName, as in xml:id or
svg:rect, it refers to a name with the local name localName and the namespace given by the prefix, as
defined by the following table:
xmlhttp://www.w3.org/XML/1998/namespacehtmlhttp://www.w3.org/1999/xhtmlsvghttp://www.w3.org/2000/svgAttribute names are said to be XML-compatible if they
match the Name production defined in XML, they contain no
U+003A COLON (:) characters, and their first three characters are
not an ASCII case-insensitive match for the string
"xml". [XML]
The term root element, when not explicitly qualified as referring to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself if it has no ancestors. When the node is a part of the document, then that is indeed the document's root element; however, if the node is not currently part of the document tree, the root element will be an orphaned node.
A node's home subtree is the subtree rooted at that node's root element.
The Document of a Node (such as an
element) is the Document that the Node's
ownerDocument DOM attribute returns.
An element is said to have been inserted into a document when its root
element changes and is now the document's root
element. If a Node is in a Document
then that Document is always the Node's
Document, and the Node's ownerDocument DOM attribute thus always returns that
Document.
The term tree order means a pre-order, depth-first
traversal of DOM nodes involved (through the parentNode/childNodes
relationship).
When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.
The term text node refers to any Text
node, including CDATASection nodes; specifically, any
Node with node type TEXT_NODE (3)
or CDATA_SECTION_NODE (4). [DOM3CORE]
The construction "a Foo object", where
Foo is actually an interface, is sometimes used instead
of the more accurate "an object implementing the interface
Foo".
A DOM attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.
If a DOM object is said to be live, then that means that any attributes returning that object must always return the same object (not a new object each time), and the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.
The terms fire and dispatch are used interchangeably in the context of events, as in the DOM Events specifications. [DOM3EVENTS]
The term plugin is used to mean any content handler, typically a third-party content handler, for Web content types that are not supported by the user agent natively, or for content types that do not expose a DOM, that supports rendering the content as part of the user agent's interface.
One example of a plugin would be a PDF viewer that is instantiated in a browsing context when the user navigates to a PDF file. This would count as a plugin regardless of whether the party that implemented the PDF viewer component was the same as that which implemented the user agent itself. However, a PDF viewer application that launches separate from the user agent (as opposed to using the same interface) is not a plugin by this definition.
This specification does not define a mechanism for interacting with plugins, as it is expected to be user-agent- and platform-specific. Some UAs might opt to support a plugin mechanism such as the Netscape Plugin API; others might use remote content converters or have built-in support for certain types. [NPAPI]
Browsers should take extreme care when interacting with external content intended for plugins. When third-party software is run with the same privileges as the user agent itself, vulnerabilities in the third-party software become as dangerous as those in the user agent.
An ASCII-compatible character encoding is one that is a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the set 0x09, 0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A.
All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]
Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.
This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).
There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.
User agents fall into several (overlapping) categories with different conformance requirements.
Web browsers that support XHTML must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.
A conforming XHTML processor would, upon
finding an XHTML script element in an XML document,
execute the script contained in that element. However, if the
element is found within a transformation expressed in XSLT
(assuming the user agent also supports XSLT), then the processor
would instead treat the script element as an opaque
element that forms part of the transform.
Web browsers that support HTML must
process documents labeled as text/html as described
in this specification, so that users can interact with them.
User agents that process HTML and XHTML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.
Typical examples of non-interactive presentation user agents are printers (static UAs) and overhead displays (dynamic UAs). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.
A non-interactive but dynamic presentation UA would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the UA would not need to support any of the focus-related DOM APIs.
Implementations that do not support scripting (or which have their scripting features disabled entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.
Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author's intent.
Conformance checkers must verify that a document conforms to
the applicable conformance criteria described in this
specification. Automated conformance checkers are exempt from
detecting errors that require interpretation of the author's
intent (for example, while a document is non-conforming if the
content of a blockquote element is not a quote,
conformance checkers running without the input of human judgement
do not have to check that blockquote elements only
contain quoted material).
Conformance checkers must check that the input document conforms when parsed without a browsing context (meaning that no scripts are run, and that the parser's scripting flag is disabled), and should also check that the input document conforms when parsed with a browsing context in which scripts execute, and that the scripts never cause non-conforming states to occur other than transiently during script execution itself. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [HALTINGPROBLEM])
The term "HTML5 validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.
XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.
To put it another way, there are three types of conformance criteria:
A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.
Applications and tools that process HTML and XHTML documents for reasons other than to either render the documents or check them for conformance should act in accordance to the semantics of the documents that they process.
A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.
Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.
Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent.
For example, it is not conforming to use an
address element for arbitrary contact information;
that element can only be used for marking up contact information
for the author of the document or section. However, since an
authoring tool is likely unable to determine the difference, an
authoring tool is exempt from that requirement.
In terms of conformance checking, an editor is therefore required to output documents that conform to the same extent that a conformance checker will verify.
When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e. an editing tool is allowed to round-trip erroneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.
Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).
The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.
However, WYSIWYG tools are legitimate. WYSIWYG tools should use
elements they know are appropriate, and should not use elements
that they do not know to be appropriate. This might in certain
extreme cases mean limiting the use of flow elements to just a few
elements, like div, b, i,
and span and making liberal use of the style attribute.
All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.
Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. The former category of requirements are requirements on documents and authoring tools. The second category are requirements on user agents.
Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)
User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML (referred to as XHTML5), and one using a custom format inspired by SGML (referred to as HTML5). Implementations may support only one of these two formats, although supporting both is encouraged.
Such XML documents may contain a DOCTYPE if desired,
but this is not required to conform to this specification.
According to the XML specification, XML processors
are not guaranteed to process the external DTD subset referenced in
the DOCTYPE. This means, for example, that using entity references
for characters in XHTML documents is unsafe (except for <, >, &, " and
').
The language in this specification assumes that the user agent expands all entity references, and therefore does not include entity reference nodes in the DOM. If user agents do include entity reference nodes in the DOM, then user agents must handle them as if they were fully expanded when implementing this specification. For example, if a requirement talks about an element's child text nodes, then any text nodes that are children of an entity reference that is a child of that element would be used as well. Entity references to unknown entities must be treated as if they contained just an empty text node for the purposes of the algorithms defined in this specification.
This specification relies on several other underlying specifications.
Implementations that support XHTML5 must support some version of XML, as well as its corresponding namespaces specification, because XHTML5 uses an XML serialization with namespaces. [XML] [XMLNAMES]
The Document Object Model (DOM) is a representation — a model — of a document and its content. The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM. [DOM3CORE]
Implementations must support some version of DOM Core and DOM Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM Core interfaces. [DOM3CORE] [DOM3EVENTS]
Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification, as this specification uses that specification's terminology. [WebIDL]
Implementations must support some version of the Media Queries language. [MQ]
This specification does not require support of any particular network transport protocols, style sheet language, scripting language, or any of the DOM and WebAPI specifications beyond those described above. However, the language described by this specification is biased towards CSS as the styling language, ECMAScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.
This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.
this section will be removed at some point
Some elements are defined in terms of their DOM
textContent attribute. This is an attribute
defined on the Node interface in DOM3 Core. [DOM3CORE]
The interface DOMTimeStamp is defined in
DOM3 Core. [DOM3CORE]
The rules for handling alternative style sheets are defined in the CSS object model specification. [CSSOM]
This section will eventually be removed in favour of WebIDL.
A lot of arrays/lists/collections in this spec assume zero-based indexes but use the term "indexth" liberally. We should define those to be zero-based and be clearer about this.
Unless otherwise specified, if a DOM attribute that is a floating
point number type (float) is assigned an
Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be
raised.
Unless otherwise specified, if a method with an argument that is a
floating point number type (float) is passed
an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be
raised.
Unless otherwise specified, if a method is passed fewer
arguments than is defined for that method in its IDL definition,
a NOT_SUPPORTED_ERR exception must be
raised.
Unless otherwise specified, if a method is passed more arguments than is defined for that method in its IDL definition, the excess arguments must be ignored.
This specification defines several comparison operators for strings.
Comparing two strings in a case-sensitive manner means comparing them exactly, codepoint for codepoint.
Comparing two strings in a ASCII case-insensitive manner means comparing them exactly, codepoint for codepoint, except that the characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) are considered to also match.
Comparing two strings in a compatibility caseless manner means using the Unicode compatibility caseless match operation to compare the two strings. [UNICODECASE]
Converting a string to uppercase means replacing all characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z) with the corresponding characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
Converting a string to lowercase means replacing all characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) with the corresponding characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z).
A string pattern is a prefix match for a string s when pattern is not longer than s and truncating s to pattern's length leaves the two strings as matches of each other.
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.
Need to go through the whole spec and make sure all the attribute values are clearly defined either in terms of microsyntaxes or in terms of other specs, or as "Text" or some such.
The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).
The White_Space characters are those that have the Unicode property "White_Space". [UNICODE]
Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.
For parsers based on this pattern, a step that requires the user agent to collect a sequence of characters means that the following algorithm must be run, with characters being the set of characters that can be collected:
Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.
Let result be the empty string.
While position doesn't point past the end of input and the character at position is one of the characters, append that character to the end of result and advance position to the next character in input.
Return result.
The step skip whitespace means that the user agent must collect a sequence of characters that are space characters. The step skip White_Space characters means that the user agent must collect a sequence of characters that are White_Space characters. In both cases, the collected characters are not used. [UNICODE]
When a user agent is to strip line breaks from a string, the user agent must remove any U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters from that string.
The codepoint length of a string is the number of Unicode codepoints in that string.
A number of attributes in HTML5 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.
A string is a valid non-negative integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
A valid non-negative integer represents the number that is represented in base ten by that string of digits.
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 either return zero, a positive integer, or an error. Leading spaces are ignored. Trailing spaces and indeed any trailing garbage characters are ignored.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let value have the value 0.
If position is past the end of input, return an error.
If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.
If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):
Return value.
A string is a valid integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), 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.
The rules for parsing integers are similar to the rules for non-negative integers, and 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 either return an integer or an error. Leading spaces are ignored. Trailing spaces and trailing garbage characters are ignored.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let value have the value 0.
Let sign have the value "positive".
If position is past the end of input, return an error.
If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:
If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.
If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):
If sign is "positive", return value, otherwise return 0-value.
A string is a valid floating point number if it consists of:
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). If there is no E, then the exponent is treated as zero.
The rules for parsing floating point number values are as given in the following algorithm. As with the previous algorithms, when this one is invoked, the steps must be followed in the order given, aborting at the first step that returns something. This algorithm will either return a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let value have the value 1.
Let divisor have the value 1.
Let exponent have the value 1.
If position is past the end of input, return an error.
If the character indicated by position is a U+002D HYPHEN-MINUS ("-") character:
If the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the resulting sequence as a base-ten integer. Multiply value by that integer.
If the character indicated by position is a U+002E FULL STOP ("."), run these substeps:
Advance position to the next character.
If position is past the end of input, or if the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return value.
Fraction loop: Multiply divisor by ten.
Advance position to the next character.
If position is past the end of input, then return value.
If the character indicated by position is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), return to the step labeled fraction loop in these substeps.
If the character indicated by position is a U+0065 LATIN SMALL LETTER E character or a U+0045 LATIN CAPITAL LETTER E character, run these substeps:
Advance position to the next character.
If position is past the end of input, then return value.
If the character indicated by position is a U+002D HYPHEN-MINUS ("-") character:
If position is past the end of input, then return value.
If the character indicated by position is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return value.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the resulting sequence as a base-ten integer. Multiply exponent by that integer.
Multiply value by ten raised to the exponentth power.
Return value.
The algorithms described in this section are used by
the progress and meter elements.
A valid denominator punctuation character is one of the characters from the table below. There is a value associated with each denominator punctuation character, as shown in the table below.
| Denominator Punctuation Character | Value | |
|---|---|---|
| U+0025 PERCENT SIGN | % | 100 |
| U+066A ARABIC PERCENT SIGN | ٪ | 100 |
| U+FE6A SMALL PERCENT SIGN | ﹪ | 100 |
| U+FF05 FULLWIDTH PERCENT SIGN | ％ | 100 |
| U+2030 PER MILLE SIGN | ‰ | 1000 |
| U+2031 PER TEN THOUSAND SIGN | ‱ | 10000 |
The steps for finding one or two numbers of a ratio in a string are as follows:
The algorithm to find a number is as follows. It is given a string and a starting position, and returns either nothing, a number, or an error condition.
rules for parsing dimension values (only used by height/width on img, embed, object — lengths in css pixels or percentages)
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.
The rules for parsing a list of integers are as follows:
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let numbers be an initially empty list of integers. This list will be the result of this algorithm.
If there is a character in the string input at position position, and it is either a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then advance position to the next character in input, or to beyond the end of the string if there are no more characters.
If position points to beyond the end of input, return numbers and abort.
If the character in the string input at position position is a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then return to step 4.
Let negated be false.
Let value be 0.
Let started be false. This variable is
set to true when the parser sees a number or a "-" character.
Let got number be false. This variable is set to true when the parser sees a number.
Let finished be false. This variable is set to true to switch parser into a mode where it ignores characters until the next separator.
Let bogus be false.
Parser: If the character in the string input at position position is:
Follow these substeps:
Follow these substeps:
Follow these substeps:
1,2,x,4".Follow these substeps:
Follow these substeps:
Advance position to the next character in input, or to beyond the end of the string if there are no more characters.
If position points to a character (and not to beyond the end of input), jump to the big Parser step above.
If negated is true, then negate value.
If got number is true, then append value to the numbers list.
Return the numbers list and abort.
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 U+0030 DIGIT ZERO to U+0039 DIGIT NINE, used to express numbers in base ten.
A month consists of a specific proleptic Gregorian date with no timezone 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:
The rules to parse a month string are as follows. This will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a month component to obtain year and month. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Return year and month.
The rules to parse a month component, given an input string and a position, are as follows. This will either return 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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
If year is not a number greater than zero, then fail.
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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.
If month is not a number in the range 1 ≤ month ≤ 12, then fail.
Return year and month.
A date consists of a specific proleptic Gregorian date with no timezone 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:
The rules to parse a date string are as follows. This will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let date be the date with year year, month month, and day day.
Return date.
The rules to parse a date component, given an input string and a position, are as follows. This will either return 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.
Parse a month component to obtain year and month. If this returns nothing, then fail.
Let maxday be the number of days in month month of year year.
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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.
If day is not a number in the range 1 ≤ month ≤ maxday, then fail.
Return year, month, and day.
A time consists of a specific time with no timezone 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:
The second component cannot be 60 or 61; leap seconds cannot be represented.
The rules to parse a time string are as follows. This will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let time be the time with hour hour, minute minute, and second second.
Return time.
The rules to parse a time component, given an input string and a position, are as follows. This will either return 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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the hour.
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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the minute.
Let second be a string with the value "0".
If position is not beyond the end of input and the character at position is a U+003A COLON, then run these substeps:
Advance position to the next character in input.
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 two characters both in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then fail.
Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or U+002E FULL STOP characters. If the collected sequence has more than one U+002E FULL STOP characters, or if the last character in the sequence is a U+002E FULL STOP character, then fail. Otherwise, let the collected string be second instead of its previous value.
Interpret second as a base-ten number (possibly with a fractional part). Let second be that number instead of the string version.
If second is not a number in the range 0 ≤ second < 60, then fail.
Return hour, minute, and second.
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:
The rules to parse a local date and time string are as follows. This will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is beyond the end of input or if the character at position is not a U+0054 LATIN CAPITAL LETTER T character then fail. Otherwise, move position forwards one character.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let date be the date with year year, month month, and day day.
Let time be the time with hour hour, minute minute, and second second.
Return date and time.
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, consisting of a number of hours and minutes. [GREGORIAN]
A string is a valid global date and time string representing a date, time, and a timezone offset if it consists of the following components in the given order:
This format allows for time zone offsets from -23:59 to +23:59. In practice, however, the range of actual time zones is -12:00 to +14:00, and the minutes component of actual time zones is always either 00, 30, or 45.
The following are some examples of dates written as valid global date and time strings.
0037-12-13T00:00Z"1979-10-14T12:00:00.001-04:00"8592-01-01T02:09+02:09"Several things are notable about these dates:
The rules to parse a global date and time string are as follows. This will either return a time in UTC, with associated timezone information for round tripping 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is beyond the end of input or if the character at position is not a U+0054 LATIN CAPITAL LETTER T character then fail. Otherwise, move position forwards one character.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is beyond the end of input, then fail.
Parse a timezone component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC timezone.
Let timezone be timezonehours hours and timezoneminutes minutes from UTC.
Return time and timezone.
The rules to parse a timezone component, given an input string and a position, are as follows. This will either return timezone hours and timezone 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.
If the character at position is a U+005A LATIN CAPITAL LETTER Z, then:
Let timezonehours be 0.
Let timezoneminutes be 0.
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 ("-"), then:
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".
Advance position to the next character in input.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezonehours.
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.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezoneminutes.
Return timezonehours and timezoneminutes.
A week consists of a week-year number and a week number representing a seven day period. Each week-year in this calendaring system has either 52 weeks or 53 weeks, as defined below. A week is a seven-day period. The week 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 that corresponds to a year year in the proleptic Gregorian calendar that has a Thursday as its first day (January 1st), and a week-year year where year is a number divisible by 400, or a number divisible by 4 but not by 100, has 53 weeks. 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 year is the week that contains the first Thursday of the Gregorian year year.
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:
The rules to parse a week string are as follows. This will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
If year is not a number greater than zero, then fail.
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.
If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character, then fail. Otherwise, move position forwards one character.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the week.
Let maxweek be the week number of the last day of year year.
If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.
If position is not beyond the end of input, then fail.
Return the week-year number year and the week number week.
A date or time string consists of either a date, a time, or a global date and time.
A string is a valid date or time string if it is also one of the following:
A string is a valid date or time string in content if it consists of zero or more White_Space characters, followed by a valid date or time string, followed by zero or more further White_Space characters.
The rules to parse a date or time string are as follows. The algorithm is invoked with a flag indicating if the in attribute variant or the in content variant is to be used. The algorithm will either return 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.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
For the in content variant: skip White_Space characters.
Set start position to the same position as position.
Set the date present and time present flags to true.
Parse a date component to obtain year, month, and day. If this fails, then set the date present flag to false.
If date present is true, and position is not beyond the end of input, and the character at position is a U+0054 LATIN CAPITAL LETTER T 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 not a U+0054 LATIN CAPITAL LETTER T character, then set time present to false.
Otherwise, if date present is false, set position back to the same position as start position.
If the time present flag is true, then parse a time component to obtain hour, minute, and second. If this returns nothing, then set the time present flag to false.
If both the date present and time present flags are false, then fail.
If the time present flag is true, but position is beyond the end of input, then fail.
If the date present and time present flags are both true, parse a timezone component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
For the in content variant: skip White_Space characters.
If position is not beyond the end of input, then fail.
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 timezonehours hours and timezoneminutes minutes, that moment in time being a moment in the UTC timezone; let timezone be timezonehours hours and timezoneminutes minutes from UTC; and return time and timezone.
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 NUMBER SIGN (#) character, and the remaining six characters are all in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN SMALL LETTER A .. 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 .. U+0046 LATIN CAPITAL LETTER F.
The rules for parsing simple color 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 either return a simple color or an error.
Let input be the string being parsed.
If input is not exactly seven characters long, then return an error.
If the first character in input is not a U+0023 NUMBER SIGN (#) character, then return an error.
If the last six characters of input are not all in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, then return an error.
Let result be a simple color.
Interpret the second and third characters as a hexadecimal number and let the result be the red component of result.
Interpret the fourth and fifth characters as a hexadecimal number and let the result be the green component of result.
Interpret the sixth and seventh characters as a hexadecimal number and let the result be the blue component of result.
Return result.
The rules for serialising simple color values given a simple color are as given in the following algorithm:
Let result be a string consisting of a single U+0023 NUMBER SIGN (#) character.
Convert the red, green, and blue components in turn to two-digit hexadecimal numbers using the digits U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9) and U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, zero-padding if necessary, and append these numbers to result, in the order red, green, blue.
Return result, which will be a valid lowercase simple color.
The 2D graphics context has a separate color syntax that also handles opacity.
Some obsolete legacy attributes parse colors in a more complicated manner.
A set of space-separated tokens is a set of zero or more words 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 words are duplicated.
An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the words 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.
When a user agent has to split a string on spaces, it must use the following algorithm:
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let tokens be a list of tokens, initially empty.
While position is not past the end of input:
Collect a sequence of characters that are not space characters.
Add the string collected in the previous step to tokens.
Return tokens.
When a user agent has to remove a token from a string, it must use the following algorithm:
Let input be the string being modified.
Let token be the token being removed. It will not contain any space characters.
Let output be the output string, initially empty.
Let position be a pointer into input, initially pointing at the start of the string.
If position is beyond the end of input, set the string being modified to output, and abort these steps.
If the character at position is a space character:
Append the character at position to the end of output.
Increment position so it points at the next character in input.
Return to step 5 in the overall set of steps.
Otherwise, the character at position is the first character of a token. Collect a sequence of characters that are not space characters, and let that be s.
If s is exactly equal to token, then:
Skip whitespace (in input).
Remove any space characters currently at the end of output.
If position is not past the end of input, and output is not the empty string, append a single U+0020 SPACE character at the end of output.
Otherwise, append s to the end of output.
Return to step 6 in the overall set of steps.
This causes any occurrences of the token to be removed from the string, and any spaces that were surrounding the token to be collapsed to a single space, except at the start and end of the string, where such spaces are removed.
We should allow whitespace around commas, and leading/trailing whitespace.
A set of comma-separated tokens is a set of 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, none of which are U+002C COMMA
characters (,).
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.
When a user agent has to split a string on commas, it must use the following algorithm:
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let tokens be a list of tokens, initially empty.
Token: If position is past the end of input, jump to the last step.
Collect a sequence of characters that are not
U+002C COMMA characters (,).
Add the string collected in the previous step (which might be the empty string) to tokens.
If position is not past the end of input, then the character at position is a U+002C COMMA character (,); advance position past that
character.
Jump back to the step labeled token.
Return tokens.
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-insensitively 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 one of the keywords in some
cases. For example the contenteditable attribute has
two states: true, matching the true
keyword and the empty string, false, matching false and all other keywords (it's the invalid
value default). It could further be thought of as having a
third state inherit, which would be the default when the
attribute is not specified at all (the missing value
default), but for various reasons that isn't the way this
specification actually defines it.
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 in the document with type type.
The rules for parsing a hash-name reference to an element of type type are as follows:
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 and abort these steps.
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.
Return the first element of type type
that has an id attribute whose value
is a case-sensitive match for s or
a name attribute whose value is a
compatibility caseless match for s.
This specification defines the term URL, and defines various algorithms for dealing with URLs, because for historical reasons the rules defined by the URI and IRI specifications are not a complete description of what HTML user agents need to implement to be compatible with Web content.
A URL is a string used to identify a resource.
A URL is a valid URL if at least one of the following conditions holds:
The URL is a valid IRI reference and it has no query component. [RFC3987]
The URL is a valid IRI reference and its query component contains no unescaped non-ASCII characters. [RFC3987]
The URL is a valid IRI reference and the character encoding of
the URL's Document is UTF-8 or UTF-16. [RFC3987]
A URL has an associated URL character encoding, determined as follows:
Document, and the URL character
encoding is the document's character encoding.The term "URL" in this specification is used in a manner distinct from the precise technical meaning it is given in RFC 3986. Readers familiar with that RFC will find it easier to read this specification if they pretend the term "URL" as used herein is really called something else altogether.
To parse a URL url into its component parts, the user agent must use the following steps:
Strip leading and trailing space characters from url.
Parse url in the manner defined by RFC 3986, with the following exceptions:
If url doesn't match the <URI-reference> production, even after the above changes are made to the ABNF definitions, then parsing the URL fails with an error. [RFC3986]
Otherwise, parsing url was successful; the components of the URL are substrings of url defined as follows:
The substring matched by the <scheme> production, if any.
The substring matched by the <host> production, if any.
The substring matched by the <port> production, if any.
If there is a <scheme> component and a <port> component and the port given by the <port> component is different than the default port defined for the protocol given by the <scheme> component, then <hostport> is the substring that starts with the substring matched by the <host> production and ends with the substring matched by the <port> production, and includes the colon in between the two. Otherwise, it is the same as the <host> component.
The substring matched by one of the following productions, if one of them was matched:
The substring matched by the <query> production, if any.
The substring matched by the <fragment> production, if any.
The substring that follows the substring matched by the <authority> production, or the whole string if the <authority> production wasn't matched.
Relative URLs are resolved relative to a base URL. The base URL of a URL is the absolute URL obtained as follows:
The base URL is the script's base URL.
The base URL is the base URI of the element that the
attribute is on, as defined by the XML Base specification, with
the base URI of the document entity being defined as the
document base URL of the Document that
owns the element.
For the purposes of the XML Base specification, user agents
must act as if all Document objects represented XML
documents.
It is p