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W3C

XML Path Language (XPath) 4.0 WG Review Draft

W3C Editor's Draft 23 February 2026

This version:
https://qt4cg.org/specifications/xpath-40/
Most recent version of XPath:
https://qt4cg.org/specifications/xpath-40/
Most recent Recommendation of XPath:
https://www.w3.org/TR/2017/REC-xpath-31-20170321/
Editor:
Michael Kay, Saxonica <mike@saxonica.com>

Please check the errata for any errors or issues reported since publication.

See also translations.

This document is also available in these non-normative formats: XML.

Copyright © 2000 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and document use rules apply.

Abstract

XPath 4.0 is an expression language that allows the processing of values conforming to the data model defined in [XQuery and XPath Data Model (XDM) 4.0]. The name of the language derives from its most distinctive feature, the path expression, which provides a means of hierarchic addressing of the nodes in an XML tree. As well as modeling the tree structure of XML, the data model also includes atomic items, function items, maps, arrays, and sequences. This version of XPath supports JSON as well as XML, and adds many new functions in [XQuery and XPath Functions and Operators 4.0].

XPath 4.0 is a superset of XPath 3.1. A detailed list of changes made since XPath 3.1 can be found in I Change Log.

Status of this Document

This is a draft prepared by the QT4CG (officially registered in W3C as the XSLT Extensions Community Group). Comments are invited.

Dedication

The publications of this community group are dedicated to our co-chair, Michael Sperberg-McQueen (1954–2024).

Michael was central to the development of XML and many related technologies. He brought a polymathic breadth of knowledge and experience to everything he did. This, combined with his indefatigable curiosity and appetite for learning, made him an invaluable contributor to our project, along with many others. We have lost a brilliant thinker, a patient teacher, and a loyal friend.

3 Types

As noted in 2.1.2 Values, every value in XPath 4.0 is regarded as a sequence of zero, one, or more items. The type system of XPath 4.0, described in this section, classifies the kinds of value that the language can handle, and the operations permitted on different kinds of value.

The type system of XPath 4.0 is related to the type system of [XML Schema 1.0] or [XML Schema 1.1] in two ways:

This chapter of the specification starts by defining sequence types and item types, which describe the range of values that can be bound to variables, used in expressions, or passed to functions. It then describes how these relate to schema types, that is, the simple and complex types defined in an XSD schema.

Note:

In many situations the terms item type and sequence type are used interchangeably to refer either to the type itself, or to the syntactic construct that designates the type: so in the expression $x instance of xs:string*, the construct xs:string* uses the SequenceType syntax to designate a sequence type whose instances are sequences of strings. When more precision is required, the specification is careful to use the terms item type and sequence type to refer to the actual types, while using the production names ItemType and SequenceType to refer to the syntactic designators of these types.

3.2 Item Types

[Definition: An item type is a type that can be expressed using the ItemType syntax, which forms part of the SequenceType syntax. Item types match individual items.]

Note:

While this definition is adequate for the purpose of defining the syntax of XPath 4.0, it ignores the fact that there are also item types that cannot be expressed using XPath 4.0 syntax: specifically, item types that reference an anonymous simple type or complex type defined in a schema. Such types can appear as type annotations on nodes following schema validation.

In most cases, the set of items matched by an item type consists either exclusively of atomic items, exclusively of nodes, or exclusively of function itemsDM. Exceptions include the generic types item(), which matches all items, xs:error, which matches no items, and choice item types, which can match any combination of types.

[Definition: An item type designator is a syntactic construct conforming to the grammar rule ItemType. An item type designator is said to designate an item type.]

Note:

Two item type designators may designate the same item type. For example, element() and element(*) are equivalent, as are attribute(A) and attribute(A, xs:anySimpleType).

Lexical QNames appearing in an item type designator are expanded using the default type namespace rule. Equality of QNames is defined by the eq operator.

ItemType::=AnyItemTest | TypeName | KindTest | FunctionType | MapType | ArrayType | RecordType | EnumerationType | ChoiceItemType
AnyItemTest::="item" "(" ")"
TypeName::=EQName
EQName::=QName | URIQualifiedName
KindTest::=DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
DocumentTest::="document-node" "(" (ElementTest | SchemaElementTest | NameTestUnion)? ")"
ElementTest::="element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
SchemaElementTest::="schema-element" "(" ElementName ")"
NameTestUnion::=(NameTest ++ "|")
NameTest::=EQName | Wildcard
Wildcard::="*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
AttributeTest::="attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
SchemaAttributeTest::="schema-attribute" "(" AttributeName ")"
PITest::="processing-instruction" "(" (NCName | StringLiteral)? ")"
StringLiteral::=AposStringLiteral | QuotStringLiteral
/* ws: explicit */
CommentTest::="comment" "(" ")"
TextTest::="text" "(" ")"
NamespaceNodeTest::="namespace-node" "(" ")"
AnyKindTest::="node" "(" ")"
FunctionType::=AnyFunctionType
| TypedFunctionType
MapType::=AnyMapType | TypedMapType
ArrayType::=AnyArrayType | TypedArrayType
RecordType::=AnyRecordType | TypedRecordType
EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"
ChoiceItemType::="(" (ItemType ++ "|") ")"

This section defines the syntax and semantics of different ItemTypes in terms of the values that they match.

Note:

For an explanation of the EBNF grammar notation (and in particular, the operators ++ and **), see A.1 EBNF.

An item type designator written simply as an EQName (that is, a TypeName) is interpreted as follows:

  1. If the name is written as a lexical QName, then it is expanded using the default type namespace rule.

  2. If the expanded name matches a named item type in the static context, then it is taken as a reference to the corresponding item type. The rules that apply are the rules for the expanded item type definition.

  3. Otherwise, it must match the name of a type in the in-scope schema types in the static context: specifically, an atomic type or a pure union type. See 3.5 Schema Types for details.

    Note:

    A name in the xs namespace will always fall into this category, since the namespace is reserved. See 2.1.3 Namespaces and QNames.

  4. If the name cannot be resolved to a type, a static error is raised [err:XPST0051].

3.2.6 Enumeration Types

Changes in 4.0 ⬇ ⬆

  1. Enumeration types are added as a new kind of ItemType, constraining the value space of strings.  [Issue 688 PR 691 10 October 2023]

[Definition: An EnumerationType accepts a fixed set of string values.]

EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"
StringLiteral::=AposStringLiteral | QuotStringLiteral
/* ws: explicit */

An enumeration type has a value space consisting of a set of xs:string values. When matching strings against an enumeration type, strings are always compared using the Unicode codepoint collation.

For example, if an argument of a function declares the required type as enum("red", "green", "blue"), then the string "green" is accepted, while "yellow" is rejected with a type error.

Technically, enumeration types are defined as follows:

  • [Definition: An enumeration type with a single enumerated value (such as enum("red")) is an anonymous atomic type derived from xs:string by restriction using an enumeration facet that permits only the value "red". This is referred to as a singleton enumeration type.] It is equivalent to the XSD-defined type:

    <xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:enumeration value="red"/>
  </xs:restriction>
</xs:simpleType>

  • Two singletonsingleton enumeration types enumeration types are the same type if and only if they have the same (single) enumerated value, as determined using the Unicode codepoint collation.

  • An enumeration type with multiple enumerated values is a union of singleton enumeration typessingleton enumeration types, so enum("red", "green", "blue") is equivalent to (enum("red") | enum("green") | enum("blue")).

  • In consequence, an enumeration type T is a subtype of an enumeration type U if the enumerated values of T are a subset of the enumerated values of U: see 3.3.2 Subtypes of Item Types.

An enumeration type is thus a generalized atomic type.

It follows from these rules that an atomic item will only satisfy an instance of test if it has the correct type annotation, and this can only be achieved using an explicit cast or constructor function. So the expression "red" instance of enum("red", "green", "blue") returns false. However, the coercion rules ensure that where a variable or function declaration specifies an enumeration type as the required type, a string (or indeed an xs:untypedAtomic or xs:anyURI value) equal to one of the enumerated values will be accepted.

Note:

Some consequences of these rules may not be immediately apparent.

Suppose that an XQuery query contains the declarations:

declare type my:color := enum("red", "green", "orange");
declare type my:fruit := enum("apple", "orange", "banana");
declare variable $orange-color as my:color := "orange";
declare variable $orange-fruit as my:fruit := "orange";

The same applies with the equivalent XSLT syntax:

<xsl:item-type name="my:color" as="enum('red', 'green', 'orange')"/>
<xsl:item-type name="my:fruit" as="enum('apple', 'orange', 'banana')"/>
<xsl:variable name="orange-color" as="my:color" select="'orange'"/>
<xsl:variable name="orange-fruit" as="my:fruit" select="'orange'"/>

Now, the value of $orange-color is an atomic item whose datum is the string "orange", and whose type annotation is the anonymous type designated enum("orange"). Similarly, the value of $orange-fruit is an atomic item whose datum is the string "orange", and whose type annotation is the anonymous type designated enum("orange"). That is, the values of the two variables are indistinguishable and interchangeable in every way. In particular, both values are instances of my:color, and both are instances of my:fruit.

This way of handling enumeration values has advantages and disadvantages. On the positive side, it means that enumeration subsets and supersets work cleanly: a value that is an instance of enum("red", "green", "orange") can be used where an instance of enum("red", "orange", "yellow", "green", "blue", "indigo", "violet") is expected. The downside is that labeling a string as an instance of an enumeration type does not provide type safety: a function that expects an instance of my:color can be called with any string that matches one of the required colors, whether or not it has an appropriate type annotation. A function that expects a color can be successfully called passing a fruit, if they happen to have the same name.

3.4 Coercion Rules

Changes in 4.0 ⬇ ⬆

  1. The term "function conversion rules" used in 3.1 has been replaced by the term "coercion rules".   [ PR 254 29 November 2022]

  2. The coercion rules allow “relabeling” of a supplied atomic item where the required type is a derived atomic type: for example, it is now permitted to supply the value 3 when calling a function that expects an instance of xs:positiveInteger.   [Issue 117 PR 254 29 November 2022]

  3. The coercion rules now allow any numeric type to be implicitly converted to any other, for example an xs:double is accepted where the required type is xs:double.   [Issue 980 PR 911 30 January 2024]

  4. The coercion rules now allow conversion in either direction between xs:hexBinary and xs:base64Binary.   [Issues 130 480 PR 815 7 November 2023]

  5. The coercion rules now apply recursively to the members of an array and the entries in a map.   [Issue 1318 PR 1501 29 October 2024]

  6. The coercion rules now reorder the entries in a map when the required type is a record type.   [Issue 1862 PR 1874 25 March 2025]

[Definition: The coercion rules are rules used to convert a supplied value to a required type, for example when converting an argument of a function call to the declared type of the function parameter. ] The required type is expressed as a sequence type. The effect of the coercion rules may be to accept the value as supplied, to convert it to a value that matches the required type, or to reject it with a type error.

This section defines how the coercion rules operate; the situations in which the rules apply are defined elsewhere, by reference to this section.

Note:

In previous versions of this specification, the coercion rules were referred to as the function conversion rules. The terminology has changed because the rules are not exclusively associated with functions or function calling.

If the required type is empty-sequence(), no coercion takes place (the supplied value must be an empty sequence, or a type error occurs).

In all other cases, the required sequence typeT comprises a required item typeR and an optional occurrence indicator. The coercion rules are then applied to a supplied value V and the required type T as follows:

  1. If XPath 1.0 compatibility mode is true and V is not an instance of the required type T, then the conversions defined in 3.4.1 XPath 1.0 Compatibility Rules are applied to V. Then:

  2. Each item in V is processed against the required item type R using the item coercion rules defined in 3.4.2 Item Coercion Rules, and the results are sequence-concatenated into a single sequence V′.

  3. A type error is raised if the cardinality of V′ does not match the required cardinality of T [err:XPTY0004].

3.4.2 Item Coercion Rules

The rules in this section are used to process each item J in a supplied sequence, given a required item typeR.

  1. If R is a generalized atomic type (for example, if it is an atomic type, a pure union type, or an enumeration type), and J is not an atomic item, then:

    1. J is atomized to produce a sequence of atomic items JJ.

    2. Each atomic item in JJ is coerced to the required type R by recursive application of the item coercion rules (the rules in this section) to produce a value V.

    3. The result is the sequence-concatenation of the V values.

    Note:

    For example, if J is an element with type annotation xs:integer, and R is the union type xs:numeric, then the effect is to atomize the element to an xs:integer, and then to coerce the resulting xs:integer to xs:numeric (which leaves the integer unchanged). This is not the same as attempting to coerce the element to each of the alternatives of the union type in turn, which would deliver an instance of xs:double.

  2. Otherwise, if R is a choice item type or a pure union type (which includes the case where it is an enumeration type), then:

    1. If J matches (is an instance of) one of the alternatives in R, then J is coerced to the first alternative in R that J matches.

      Note:

      There are two situations where coercing an item to a type that it already matches does not simply return the item unchanged:

      • When the required type is a typed function type (see 3.2.8.1 Function Types), then function coercion is applied to coerce J to that function type, as described in 3.4.4 Function Coercion.

      • When the required type is a record type and the supplied value is a map, then coercion may change the entry orderDM of the entries in the map.

    2. Otherwise, the item coercion rules (the rules in this section) are applied to J recursively with R set to each of the alternatives in the choice or union item type, in order, until an alternative is found that does not result in a type error; a type error is raised only if all alternatives fail.

      The error code used in the event of failure should be the error code arising from the first unsuccessful matching attempt. (The diagnostic information associated with the error may also describe how further attempts failed.)

    Note:

    Suppose the required type is (xs:integer | element(e))* and the supplied value is the sequence (<e>22</e>, 23, <f>24</f>). Item coercion is applied independently to each of the three items in this sequence. The first item matches one of the alternatives, namely element(e), so it is returned unchanged as an element node. The second item (the integer 23) also matches one of the alternatives, and is returned unchanged as an integer. The third item does not match any of the alternatives, so coercion is attempted to each one in turn. Coercion to type xs:integer succeeds (by virtue of atomization and untyped atomic conversion), so the final result is the sequence (<e>22</e>, 23, 24)

    Note:

    Suppose the required type is enum("red", "green", "blue") and the supplied value is "green". The enumeration type is defined as a choice item type whose alternatives are singleton enumerations, so the rules are applied first to the type enum("red") (which fails), and then to the type enum("green") (which succeeds). The strings in an enumeration type are required to be distinct so the order of checking is in this case immaterial. The supplied value will be accepted, and will be relabeled as an instance of enum("green"), which is treated as a schema type equivalent to a type derived from xs:string by restriction.

    Note:

    Schema-defined union types behave in exactly the same way as choice item types.

  3. If R is an atomic type and J is an atomic item, then:

    1. If J is an instance of R then it is used unchanged.

    2. If J is an instance of type xs:untypedAtomic then:

      1. If R is an enumeration type then A is cast to xs:string.

      2. If R is namespace-sensitive then a type error [err:XPTY0117] is raised.

      3. Otherwise, J is cast to type R.

    3. Otherwise, J is cast to type R.

  4. If there is an entry (from, to) in the following table such that J is an instance of from, and to is R, then J is cast to type R.

    Implicit Casting
    fromto
    xs:decimalxs:double
    xs:doublexs:decimal
    xs:decimalxs:float
    xs:floatxs:decimal
    xs:floatxs:double
    xs:doublexs:float
    xs:stringxs:anyURI
    xs:anyURIxs:string
    xs:hexBinaryxs:base64Binary
    xs:base64Binaryxs:hexBinary

    Note:

    The item type in the to column must match R exactly; however, J may belong to a subtype of the type in the from column.

    For example, an xs:NCName will be cast to type xs:anyURI, but an xs:anyURI will not be cast to type xs:NCName.

    Similarly, an xs:integer will be cast to type xs:double, but an xs:double will not be cast to type xs:integer.

  5. If R is derived from some primitive atomic type P, then J is relabeled as an instance of R if it satisfies all the following conditions:

    • J is an instance of P.

    • J is not an instance of R.

    • The datumDM of J is within the value space of R.

    Relabeling an atomic item changes the type annotation but not the datumDM. For example, the xs:integer value 3 can be relabeled as an instance of xs:unsignedByte, because the datum is within the value space of xs:unsignedByte.

    Note:

    Relabeling is not the same as casting. For example, the xs:decimal value 10.1 can be cast to xs:integer, but it cannot be relabeled as xs:integer, because its datum not within the value space of xs:integer.

    Note:

    The effect of this rule is that if, for example, a function parameter is declared with an expected type of xs:positiveInteger, then a call that supplies the literal value 3 will succeed, whereas a call that supplies -3 will fail.

    This differs from previous versions of this specification, where both these calls would fail.

    This change allows the arguments of existing functions to be defined with a more precise type. For example, the $position argument of array:get could be defined as xs:positiveInteger rather than xs:integer.

    Note:

    If T is a union type with members xs:negativeInteger and xs:positiveInteger)* and the supplied value is the sequence (20, -20), then the effect of these rules is that the first item 20 is relabeled as type xs:positiveInteger and the second item -20is relabeled as type xs:negativeInteger.

    Note:

    Promotion (for example of xs:float to xs:double) occurs only when T is a primitive type. Relabeling occurs only when T is a derived type. Promotion and relabeling are therefore never combined.

    Note:

    A singletonsingleton enumeration type enumeration type such as enum("green") is treated as an atomic type derived by restriction from xs:string; so if the xs:string value "green" is supplied in a context where the required type is enum("red", "green", "blue"), the value will be accepted and will be relabeled as an instance of enum("green").

  6. If R is an ArrayType other than array(*) and J is an array, then J is converted to a new array by converting each member to the required member type by applying the coercion rules recursively.

    Note:

    For example, if the required type is array(xs:double) and the supplied value is [ 1, 2 ], the array is converted to [ 1e0, 2e0 ].

  7. If R is a MapType other than map(*) and J is a map, then J is converted to a new map as follows:

    1. Each key in the supplied map is converted to the required map key type by applying the coercion rules. If the resulting map would contain duplicate keys, a type error is raised [err:XPTY0004].

    2. The corresponding value is converted to the required map value type by applying the coercion rules recursively.

    3. The order of entries in the map remains unchanged.

    Note:

    For example, if the required type is map(xs:string, xs:double) and the supplied value is { "x": 1, "y": 2 }, the map is converted to { "x": 1e0, "y": 2e0 }.

    Note:

    Duplicate keys can occur if the value space of the target type is more restrictive than the original type. For example, an error is raised if the map { 1.2: 0, 1.2000001: 0 }, which contains two keys of type xs:decimal, is coerced to the type map(xs:float, xs:integer).

  8. If R is a RecordType and J is a map, then J is converted to a new map as follows:

    1. The keys in the supplied map are unchanged.

    2. In any map entry whose key is equal to the name of one of the field declarations in R (under the rules of the atomic-equal function), the corresponding value is converted to the required type defined by that field declaration, by applying the coercion rules recursively (but with XPath 1.0 compatibility mode treated as false).

    3. The order of entries in the map is changed: entries whose keys correspond to the names of field declarations in R appear first, in the order of the corresponding field declarations, and (if the record type is extensible) other entries then follow retaining their relative order in J.

    Note:

    For example, if the required type is record(longitude as xs:double, latitude as xs:double) and the supplied value is { "latitude": 53.2, "longitude": 0 }, then the map is converted to { "longitude": 0.0e0, "latitude": 53.2e0 }.

  9. If R is a TypedFunctionType and J is a function item, then function coercion is applied to J.

    Note:

    Function coercion applies even if J is already an instance of R.

    Maps and arrays are functions, so function coercion applies to them as well.

  10. If, after the above conversions, the resulting item does not match the expected item type R according to the rules for SequenceType Matching, a type error is raised [err:XPTY0004].

    Note:

    Under the general rules for type errors (see 2.4.1 Kinds of Errors), a processor may report a type error during static analysis if it will necessarily occur when the expression is evaluated. For example, the function call fn:abs("beer") will necessarily fail when evaluated, because the function requires a numeric value as its argument; this may be detected and reported as a static error.

F Glossary (Non-Normative)

anonymous function

An anonymous function is a function item with no name. Anonymous functions may be created, for example, by evaluating an inline function expression or by partial function application.

application function

Application functions are function definitions written in a host language such as XQuery or XSLT whose syntax and semantics are defined in this family of specifications. Their behavior (including the rules determining the static and dynamic context) follows the rules for such functions in the relevant host language specification.

argument expression

An argument to a function call is either an argument expression or an ArgumentPlaceholder (?); in both cases it may either be supplied positionally, or identified by a name (called a keyword).

arity range

A function definition has an arity range, which is a range of consecutive non-negative integers. If the function definition has M required parameters and N optional parameters, then its arity range is from M to M+N inclusive.

array

An array is a function item that associates a set of positions, represented as positive integer keys, with values.

associated value

The value associated with a given key is called the associated value of the key.

atomic item

An atomic item is a value in the value space of an atomic type, as defined in [XML Schema 1.0] or [XML Schema 1.1].

atomic type

An atomic type is a simple schema type whose {variety}XS11-1 is atomic.

atomization

Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.1.4 fn:dataFO.

available binary resources

Available binary resources. This is a mapping of strings to binary resources. Each string represents the absolute URI of a resource. The resource is returned by the fn:unparsed-binary function when applied to that URI.

available documents

Available documents. This is a mapping of strings to document nodes. Each string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.

available item collections

Available collections. This is a mapping of strings to sequences of items. Each string represents the absolute URI of a resource. The sequence of items represents the result of the fn:collection function when that URI is supplied as the argument.

available text resources

Available text resources. This is a mapping of strings to text resources. Each string represents the absolute URI of a resource. The resource is returned by the fn:unparsed-text function when applied to that URI.

available uri collections

Available URI collections. This is a mapping of strings to sequences of URIs. The string represents the absolute URI of a resource which can be interpreted as an aggregation of a number of individual resources each of which has its own URI. The sequence of URIs represents the result of the fn:uri-collection function when that URI is supplied as the argument.

axis step

An axis step returns a sequence of nodes that are reachable from a starting node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type annotation .

binding collection

The result of evaluating the binding expression in a for expression is called the binding collection

choice item type

A choice item type defines an item type that is the union of a number of alternatives. For example the type (xs:hexBinary | xs:base64Binary) defines the union of these two primitive atomic types, while the type (map(*) | array(*)) matches any item that is either a map or an array.

coercion rules

The coercion rules are rules used to convert a supplied value to a required type, for example when converting an argument of a function call to the declared type of the function parameter.

collation

A collation is a specification of the manner in which strings and URIs are compared and, by extension, ordered. For a more complete definition of collation, see Section 5.3 Comparison of stringsFO.

comma operator

One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.

complex terminal

A complex terminal is a variable terminal whose production rule references, directly or indirectly, an ordinary production rule.

constructor function

The constructor function for a given simple type is used to convert instances of other simple types into the given type. The semantics of the constructor function call T($arg) are defined to be equivalent to the expression $arg cast as T?.

content expression

In an enclosed expression, the optional expression enclosed in curly brackets is called the content expression.

context dependent

A function definition is said to be context dependent if its result depends on the static or dynamic context of its caller. A function definition may be context-dependent for some arities in its arity range, and context-independent for others: for example fn:name#0 is context-dependent while fn:name#1 is context-independent.

context node

When the context value is a single item, it can also be referred to as the context item; when it is a single node, it can also be referred to as the context node.

context position

The context position is the position of the context value within the series of values currently being processed.

context size

The context size is the number of values in the series of values currently being processed.

context value

The context value is the value currently being processed.

current dateTime

Current dateTime. This information represents an implementation-dependent point in time during the processing of an expression, and includes an explicit timezone. It can be retrieved by the fn:current-dateTime function. If called multiple times during the execution of an expression, this function always returns the same result.

data model

XPath 4.0 operates on the abstract, logical structure of an XML document or JSON object rather than its surface syntax. This logical structure, known as the data model, is defined in [XQuery and XPath Data Model (XDM) 4.0].

decimal-separator

decimal-separator(M, R) is used to separate the integer part of the number from the fractional part. The default value for both the marker and the rendition is U+002E (FULL STOP, PERIOD, .) .

default calendar

Default calendar. This is the calendar used when formatting dates in human-readable output (for example, by the functions fn:format-date and fn:format-dateTime) if no other calendar is requested. The value is a string.

default collation

Default collation. This identifies one of the collations in statically known collations as the collation to be used by functions and operators for comparing and ordering values of type xs:string and xs:anyURI (and types derived from them) when no explicit collation is specified.

default collection

Default collection. This is the sequence of items that would result from calling the fn:collection function with no arguments.

default element namespace rule

When an unprefixed lexical QName is expanded using the default element namespace rule, then it uses the default namespace for elements and types. If this is absent, or if it takes the special value ##any, then the no-namespace rule is used.

default function namespace

Default function namespace. This is either a namespace URI, or absentDM. The namespace URI, if present, is used for any unprefixed QName appearing in a position where a function name is expected.

default function namespace rule

When an unprefixed lexical QName is expanded using the default function namespace rule, it uses the default function namespace from the static context.

default in-scope namespace

The default in-scope namespace of an element node

default language

Default language. This is the natural language used when creating human-readable output (for example, by the functions fn:format-date and fn:format-integer) if no other language is requested. The value is a language code as defined by the type xs:language.

default namespace for elements and types

Default namespace for elements and types. This is either a namespace URI, or the special value "##any", or absentDM. This indicates how unprefixed QNames are interpreted when they appear in a position where an element name or type name is expected.

default place

Default place. This is a geographical location used to identify the place where events happened (or will happen) when processing dates and times using functions such as fn:format-date, fn:format-dateTime, and fn:civil-timezone, if no other place is specified. It is used when translating timezone offsets to civil timezone names, and when using calendars where the translation from ISO dates/times to a local representation is dependent on geographical location. Possible representations of this information are an ISO country code or an Olson timezone name, but implementations are free to use other representations from which the above information can be derived. The only requirement is that it should uniquely identify a civil timezone, which means that country codes for countries with multiple timezones, such as the United States, are inadequate.

default type namespace rule

When an unprefixed lexical QName is expanded using the default type namespace rule, it uses the default namespace for elements and types. If this is absent, the no-namespace rule is used. If the default namespace for elements and types has the special value ##any, then the lexical QName refers to a name in the namespace http://www.w3.org/2001/XMLSchema.

default URI collection

Default URI collection. This is the sequence of URIs that would result from calling the fn:uri-collection function with no arguments.

delimiting terminal symbol

The delimiting terminal symbols are: !!=#$%method()**:+,-->...///::*:::=<<<<===!>=>>>=>>????[@[]```{{{|||}}}~[×÷AposStringLiteralBracedURILiteralQuotStringLiteralStringLiteral

derives from

A schema typeS1 is said to derive fromschema typeS2 if any of the following conditions is true:

digit

digit(M) is a character used in the picture string to represent an optional digit; the default value is U+0023 (NUMBER SIGN, #) .

document order

Informally, document order is the order in which nodes appear in the XML serialization of a document.

dynamically known function definitions

Dynamically known function definitions. This is a set of function definitions. It includes the statically known function definitions as a subset, but may include other function definitions that are not known statically.

dynamic context

The dynamic context of an expression is defined as information that is needed for the dynamic evaluation of an expression, beyond any information that is needed from the static context.

dynamic error

A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase.

dynamic evaluation phase

The dynamic evaluation phase is the phase during which the value of an expression is computed.

dynamic function call

A dynamic function call consists of a base expression that returns the function and a parenthesized list of zero or more arguments (argument expressions or ArgumentPlaceholders).

dynamic function call

A dynamic function call is an expression that is evaluated by calling a function item, which is typically obtained dynamically.

dynamic type

Every value matches one or more sequence types. A value is said to have a dynamic typeT if it matches (or is an instance of) the sequence type T.

effective boolean value

The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in Section 8.3.1 fn:booleanFO.

element name matching rule

When an unprefixed lexical QName is expanded using the element name matching rule rule, then it uses the default namespace for elements and types. If this is absent, then it uses the no-namespace rule. But if it takes the special value ##any, then the name is taken as matching any expanded QName with the corresponding local part, regardless of namespace: that is, the unprefixed name local is interpreted as *:local.

empty sequence

A sequence containing zero items is called an empty sequence.

enclosed expression

An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly brackets.

entry

Each key / value pair in a map is called an entry.

enumeration type

An EnumerationType accepts a fixed set of string values.

environment variables

Environment variables. This is a mapping from names to values. Both the names and the values are strings. The names are compared using an implementation-defined collation, and are unique under this collation. The set of environment variables is implementation-defined and may be empty.

error value

In addition to its identifying QName, a dynamic error may also carry a descriptive string and one or more additional values called error values.

Executable Base URI

Executable Base URI. This is an absolute URI used to resolve relative URIs during the evaluation of expressions; it is used, for example, to resolve a relative URI supplied to the fn:doc or fn:unparsed-text functions.

expanded QName

An expanded QName is a triple: its components are a prefix, a local name, and a namespace URI. In the case of a name in no namespace, the namespace URI and prefix are both absent. In the case of a name in the default namespace, the prefix is absent.

exponent-separator

exponent-separator(M, R) is used to separate the mantissa from the exponent in scientific notation. The default value for both the marker and the rendition is U+0065 (LATIN SMALL LETTER E, e) .

expression context

The expression context for a given expression consists of all the information that can affect the result of the expression.

external function

External functions can be characterized as functions that are neither part of the processor implementation, nor written in a language whose semantics are under the control of this family of specifications. The semantics of external functions, including any context dependencies, are entirely implementation-defined. In XSLT, external functions are called Section 24.1 Extension Functions XT30.

filter expression

A filter expression is an expression in the form E1[E2]: its effect is to return those items from the value of E1 that satisfy the predicate in E2.

fixed focus

A fixed focus is a focus for an expression that is evaluated once, rather than being applied to a series of values; in a fixed focus, the context value is set to one specific value, the context position is 1, and the context size is 1.

focus

The first three components of the dynamic context (context value, context position, and context size) are called the focus of the expression.

focus function

A focus function is an inline function expression in which the function signature is implicit: the function takes a single argument of type item()* (that is, any value), and binds this to the context value when evaluating the function body, which returns a result of type item()*.

function coercion

Function coercion wraps a function item in a new function whose signature is the same as the expected type. This effectively delays the checking of the argument and return types until the function is called.

function definition

A function definition contains information used to evaluate a static function call, including the name, parameters, and return type of the function.

function item

A function item is an item that can be called using a dynamic function call.

generalized atomic type

A generalized atomic type is an item type whose instances are all atomic items. Generalized atomic types include (a) atomic types, either built-in (for example xs:integer) or imported from a schema, (b) pure union types, either built-in (xs:numeric and xs:error) or imported from a schema, (c) choice item types if their alternatives are all generalized atomic types, and (d) enumeration types.

grouping-separator

grouping-separator(M, R) is used to separate groups of digits (for example as a thousands separator). The default value for both the marker and the rendition is U+002C (COMMA, ,) .

guarded

An expression E is said to be guarded by some governing condition C if evaluation of E is not allowed to fail with a dynamic error except when C applies.

host language

A host language for XPath is any environment that provides capabilities for XPath expressions to be defined and evaluated, and that supplies a static and dynamic context for their evaluation.

ignorable whitespace

Ignorable whitespace consists of any whitespace characters that may occur between terminals, unless these characters occur in the context of a production marked with a ws:explicit annotation, in which case they can occur only where explicitly specified (see A.3.5.2 Explicit Whitespace Handling).

implausible

Certain expressions, while not erroneous, are classified as being implausible, because they achieve no useful effect.

implementation defined

Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementer for each particular implementation.

implementation dependent

Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementer for any particular implementation.

implicit timezone

Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or arithmetic operation. The implicit timezone is an implementation-defined value of type xs:dayTimeDuration. See Section 3.2.7.3 Timezones XS1-2 or Section 3.3.7 dateTime XS11-2 for the range of valid values of a timezone.

infinity

infinity(R) is the string used to represent the double value infinity (INF); the default value is the string "Infinity"

inline function expression

An inline function expression, when evaluated, creates an anonymous function defined directly in the inline function expression.

in-scope attribute declarations

In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration).

in-scope element declarations

In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration).

in-scope named item types

In-scope named item types. This is a mapping from expanded QNames to named item types.

in-scope namespaces

The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI.

in-scope schema definitions

In-scope schema definitions is a generic term for all the element declarations, attribute declarations, and schema type definitions that are in scope during static analysis of an expression.

in-scope schema type

In-scope schema types. Each schema type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope schema types include the predefined schema types described in 3.5 Schema Types.

in-scope variables

In-scope variables. This is a mapping from expanded QNames to sequence types. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.

item

An item is either an atomic item, a node, or a function item.

item type

An item type is a type that can be expressed using the ItemType syntax, which forms part of the SequenceType syntax. Item types match individual items.

item type designator

An item type designator is a syntactic construct conforming to the grammar rule ItemType. An item type designator is said to designate an item type.

kind test

An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.

lexical QName

A lexical QName is a name that conforms to the syntax of the QName production

literal

A literal is a direct syntactic representation of an atomic item.

literal terminal

A literal terminal is a token appearing as a string in quotation marks on the right-hand side of an ordinary production rule.

map

A map is a function that associates a set of keys with values, resulting in a collection of key / value pairs.

mapping arrow operator

The mapping arrow operator=!> applies a function to each item in a sequence.

may

MAY means that an item is truly optional.

member

The values of an array are called its members.

method

A method is a function item that has the annotation %method.

minus-sign

minus-sign(R) is the string used to mark negative numbers; the default value is U+002D (HYPHEN-MINUS, -) .

must

MUST means that the item is an absolute requirement of the specification.

must not

MUST NOT means that the item is an absolute prohibition of the specification.

named function reference

A named function reference is an expression (written name#arity) which evaluates to a function item, the details of the function item being based on the properties of a function definition in the static context.

named item type

A named item type is an ItemType identified by an expanded QName.

namespace binding

A namespace binding is a pair comprising a namespace prefix (which is either an xs:NCName or empty), and a namespace URI.

namespace-sensitive

The namespace-sensitive types are xs:QName, xs:NOTATION, types derived by restriction from xs:QName or xs:NOTATION, list types that have a namespace-sensitive item type, and union types with a namespace-sensitive type in their transitive membership.

name test

A node test that consists only of an EQName or a Wildcard is called a name test.

NaN

NaN(R) is the string used to represent the double value NaN (not a number); the default value is the string "NaN"

node

A node is an instance of one of the node kinds defined in [TITLE OF DM40 SPEC, TITLE OF Node SECTION]DM40.

node test

A node test is a condition on the name, kind (element, attribute, text, document, comment, or processing instruction), and/or type annotation of a node. A node test determines which nodes contained by an axis are selected by a step.

no-namespace rule

When an unprefixed lexical QName is expanded using the no-namespace rule, it is interpreted as having an absent namespace URI.

non-delimiting terminal symbol

The non-delimiting terminal symbols are: ancestorancestor-or-selfandarrayasatattributecastcastablechildcommentdescendantdescendant-or-selfdivdocument-nodeelementelseempty-sequenceenumeqeveryexceptfnfollowingfollowing-or-selffollowing-siblingfollowing-sibling-or-selfforfunctiongegtidivifininstanceintersectisitemitemskeykeysleletltmapmembermodnamespacenamespace-nodenenodeoforotherwisepairsparentprecedingpreceding-or-selfpreceding-siblingpreceding-sibling-or-selfprocessing-instructionrecordreturnsatisfiesschema-attributeschema-elementselfsometextthentotreatunionvaluevaluesBinaryIntegerLiteralDecimalLiteralDoubleLiteralHexIntegerLiteralIntegerLiteralNCNameQNameURIQualifiedName

numeric

The type xs:numeric is defined as a union type with member types xs:double, xs:float, and xs:decimal. An item that is an instance of any of these types is referred to as a numeric value, and a type that is a subtype of xs:numeric is referred to as a numeric type.

ordinary production rule

An ordinary production rule is a production rule in A.1 EBNF that is not annotated ws:explicit.

partial function application

A static or dynamic function call is a partial function application if one or more arguments is an ArgumentPlaceholder.

partially applied function

A partially applied function is a function created by partial function application.

path expression

A path expression consists of a series of one or more steps, separated by / or //, and optionally beginning with / or //. A path expression is typically used to locate nodes within trees.

pattern-separator

pattern-separator(M) is a character used to separate positive and negative sub-pictures in a picture string; the default value is U+003B (SEMICOLON, ;) .

percent

percent(M, R) is used to indicate that the number is written as a per-hundred fraction; the default value for both the marker and the rendition is U+0025 (PERCENT SIGN, %) .

per-mille

per-mille(M, R) is used to indicate that the number is written as a per-thousand fraction; the default value for both the marker and the rendition is U+2030 (PER MILLE SIGN, ‰) .

pipeline operator

The pipeline operator-> evaluates an expression and binds the result to the context value before evaluating another expression.

predicate truth value

The predicate truth value of a value $V is the result of the expression if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V).

primary expression

Primary expressions are the basic primitives of the language. They include literals, variable references, context value references, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.

principal node kind

Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.

pure union type

A pure union type is a simple type that satisfies the following constraints: (a) {variety}XS11-1 is union, (b) the {facets}XS11-1 property is empty, (c) no type in the transitive membership of the union type has {variety}XS11-1list, and (d) no type in the transitive membership of the union type is a type with {variety}XS11-1union having a non-empty {facets}XS11-1 property

resolve

To resolve a relative URI$rel against a base URI $base is to expand it to an absolute URI, as if by calling the function fn:resolve-uri($rel, $base).

reverse document order

The node ordering that is the reverse of document order is called reverse document order.

same key

Two atomic items K1 and K2 have the same key value if fn:atomic-equal(K1, K2) returns true, as specified in Section 14.2.1 fn:atomic-equalFO

schema type

A schema type is a complex type or simple type as defined in the [XML Schema 1.0] or [XML Schema 1.1] specifications, including built-in types as well as user-defined types.

sequence

A sequence is an ordered collection of zero or more items.

sequence arrow operator

The sequence arrow operator=> applies a function to a supplied sequence.

sequence concatenation

The sequence concatenation of a number of sequences S1, S2, ... Sn is defined to be the sequence formed from the items of S1, followed by the items from S2, and so on, retaining order.

sequence type

A sequence type is a type that can be expressed using the SequenceType syntax. Sequence types are used whenever it is necessary to refer to a type in an XPath 4.0 expression. Since all values are sequences, every value matches one or more sequence types.

sequence type designator

A sequence type designator is a syntactic construct conforming to the grammar rule SequenceType. A sequence type designator is said to designate a sequence type.

SequenceType matching

SequenceType matching compares a value with an expected sequence type.

serialization

Serialization is the process of converting an XDM instance to a sequence of octets (step DM4 in Figure 1.), as described in [XSLT and XQuery Serialization 4.0].

singleton

A sequence containing exactly one item is called a singleton.

singleton focusenumeration type

An enumeration type with a single enumerated value (such as enum("red")) is an anonymous atomic type derived from xs:string by restriction using an enumeration facet that permits only the value "red". This is referred to as a singleton enumeration type.

singleton focus

A singleton focus is a fixed focus in which the context value is a singleton item.

stable

Document order is stable, which means that the relative order of two nodes will not change during the processing of a given expression, even if this order is implementation-dependent.

statically known collations

Statically known collations. This is an implementation-defined mapping from URI to collation. It defines the names of the collations that are available for use in processing expressions.

statically known decimal formats

Statically known decimal formats. This is a mapping from QNames to decimal formats, with one default format that has no visible name, referred to as the unnamed decimal format. Each format is available for use when formatting numbers using the fn:format-number function.

statically known function definitions

Statically known function definitions. This is a set of function definitions.

statically known namespaces

Statically known namespaces. This is a mapping from prefix to namespace URI that defines all the namespaces that are known during static processing of a given expression.

static analysis phase

The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).

Static Base URI

Static Base URI. This is an absolute URI, used to resolve relative URIs during static analysis.

static context

The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.

static error

An error that can be detected during the static analysis phase, and is not a type error, is a static error.

static function call

A static function call consists of an EQName followed by a parenthesized list of zero or more arguments.

static type

The static type of an expression is the best inference that the processor is able to make statically about the type of the result of the expression.

step

A step is a part of a path expression that generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates, working from left to right. A step may be either an axis step or a postfix expression.

string value

The string value of a node is a string and can be extracted by applying the Section 2.1.3 fn:stringFO function to the node.

substantively disjoint

Two sequence types are deemed to be substantively disjoint if (a) neither is a subtype of the other (see 3.3.1 Subtypes of Sequence Types) and (b) the only values that are instances of both types are one or more of the following:

substitution group

Substitution groups are defined in Section 2.2.2.2 Element Substitution Group XS1-1 and Section 2.2.2.2 Element Substitution Group XS11-1. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.

subtype

Given two sequence types or item types, the rules in this section determine if one is a subtype of the other. If a type A is a subtype of type B, it follows that every value matched by A is also matched by B.

subtype substitution

The use of a value that has a dynamic type that is a subtype of the expected type is known as subtype substitution.

symbol

Each rule in the grammar defines one symbol, using the following format: 

symbol ::= expression
symbol separators

Whitespace and Comments function as symbol separators. For the most part, they are not mentioned in the grammar, and may occur between any two terminal symbols mentioned in the grammar, except where that is forbidden by the /* ws: explicit */ annotation in the EBNF, or by the /* xgc: xml-version */ annotation.

system function

System functions include the functions defined in [XQuery and XPath Functions and Operators 4.0], functions defined by the specifications of a host language, constructor functions for atomic types, and any additional functions provided by the implementation. System functions are sometimes called built-in functions.

terminal

A terminal is a symbol or string or pattern that can appear in the right-hand side of a rule, but never appears on the left-hand side in the main grammar, although it may appear on the left-hand side of a rule in the grammar for terminals.

type annotation

Each element node and attribute node in an XDM instance has a type annotation (described in Section 4.1 Schema InformationDM). The type annotation of a node is a reference to a schema type.

typed value

The typed value of a node is a sequence of atomic items and can be extracted by applying the Section 2.1.4 fn:dataFO function to the node.

type error

A type error may be raised during the static analysis phase or the dynamic evaluation phase. During the static analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the dynamic evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.

URI

Within this specification, the term URI refers to a Universal Resource Identifier as defined in [RFC3986] and extended in [RFC3987] with the new name IRI.

value

In the data model, a value is always a sequence.

variable reference

A variable reference is an EQName preceded by a $-sign.

variable terminal

A variable terminal is an instance of a production rule that is not itself an ordinary production rule but that is named (directly) on the right-hand side of an ordinary production rule.

variable values

Variable values. This is a mapping from expanded QNames to values. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.

warning

In addition to static errors, dynamic errors, and type errors, an XPath 4.0 implementation may raise warnings, either during the static analysis phase or the dynamic evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.

whitespace

A whitespace character is any of the characters defined by [http://www.w3.org/TR/REC-xml/#NT-S].

wildcard-matches

In these rules, if MU and NU are NameTestUnions, then MUwildcard-matchesNU is true if every name that matches MU also matches NU.

XDM instance

The term XDM instance is used, synonymously with the term value, to denote an unconstrained sequence of items.

XPath 1.0 compatibility mode

XPath 1.0 compatibility mode.This value is true if rules for backward compatibility with XPath Version 1.0 are in effect; otherwise it is false.

xs:anyAtomicType

xs:anyAtomicType is an atomic type that includes all atomic items (and no values that are not atomic). Its base type is xs:anySimpleType from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as xs:decimal and xs:string, have xs:anyAtomicType as their base type.

xs:dayTimeDuration

xs:dayTimeDuration is derived by restriction from xs:duration. The lexical representation of xs:dayTimeDuration is restricted to contain only day, hour, minute, and second components.

xs:error

xs:error is a simple type with no value space. It is defined in Section 3.16.7.3 xs:error XS11-1 and can be used in the 3.1 Sequence Types to raise errors.

xs:untyped

xs:untyped is used as the type annotation of an element node that has not been validated, or has been validated in skip mode.

xs:untypedAtomic

xs:untypedAtomic is an atomic type that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.

xs:yearMonthDuration

xs:yearMonthDuration is derived by restriction from xs:duration. The lexical representation of xs:yearMonthDuration is restricted to contain only year and month components.

zero-digit

zero-digit(M) is the character used in the picture string to represent the digit zero; the default value is U+0030 (DIGIT ZERO, 0) . This character must be a digit (category Nd in the Unicode property database), and it must have the numeric value zero. This property implicitly defines the ten Unicode characters that are used to represent the values 0 to 9 in the function output: Unicode is organized so that each set of decimal digits forms a contiguous block of characters in numerical sequence. Within the picture string any of these ten character can be used (interchangeably) as a place-holder for a mandatory digit. Within the final result string, these ten characters are used to represent the digits zero to nine.