XML Path Language (XPath) 2.0 (Second Edition)

In the operator mapping tables, the term Gregorian refers to the types xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gDay, and xs:gMonth.

Lexically, a QName consists of an optional namespace prefix and a local name. If the namespace prefix is present, it is separated from the local name by a colon.

During evaluation of an expression, it is sometimes necessary to determine whether a value with a known dynamic type "matches" an expected sequence type. This process is known as SequenceType matching.

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.

The term XDM instance is used, synonymously with the term value, to denote an unconstrained sequence of nodes and/or atomic values in the data model.

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.

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

Atomization of a sequence is defined as the result of invoking the fn:data function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)].

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

Available documents. This is a mapping of strings onto document nodes. The 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.

An axis step returns a sequence of nodes that are reachable from the context 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.

Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri function.)

The built-in functions supported by XPath are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)].

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 [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)].

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.

The constructor function for a given type is used to convert instances of other atomic 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?).

The context item is the item currently being processed. An item is either an atomic value or a node.

Context item static type. This component defines the static type of the context item within the scope of a given expression.

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

The context position is the position of the context item within the sequence of items currently being processed.

The context size is the number of items in the sequence of items currently being processed.

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 invoked multiple times during the execution of an expression, this function always returns the same result.

XPath operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure, known as the data model, is defined in [XQuery 1.0 and XPath 2.0 Data Model (Second Edition)].

For a given node in an XDM instance, the data model schema is defined as the schema from which the type annotation of that node was derived.

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

Default element/type namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.

Default function namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where a function name is expected.

The delimiting terminal symbols are: "!=", StringLiteral, "$", "(", ")", "*", "+", (comma), "-", (dot), "..", "/", "//", (colon), "::", "<", "<<", "<=", "=", ">", ">=", ">>", "?", "@", "[", "]", "|"

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

The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.

A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase. Numeric overflow is an example of a dynamic error.

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

A dynamic type is associated with each value as it is computed. The dynamic type of a value may be more specific than the static type of the expression that computed it (for example, the static type of an expression might be xs:integer*, denoting a sequence of zero or more integers, but at evaluation time its value may have the dynamic type xs:integer, denoting exactly one integer.)

The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)].

A sequence containing zero items is called an empty sequence.

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

An expanded QName consists of an optional namespace URI and a local name. An expanded QName also retains its original namespace prefix (if any), to facilitate casting the expanded QName into a string.

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

A filter expression consists simply of a primary expression followed by zero or more predicates. The result of the filter expression consists of the items returned by the primary expression, filtered by applying each predicate in turn, working from left to right.

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

Function implementations. Each function in function signatures has a function implementation that enables the function to map instances of its parameter types into an instance of its result type.

Function signatures. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters).

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.2.4.2 Explicit Whitespace Handling).

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 implementor for any particular implementation.

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

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 [XML Schema] for the range of legal values of a timezone.

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. 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).

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, thus defining the set of namespace prefixes that are available for interpreting QNames within the scope of the element. For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.

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

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 2.5.1 Predefined Schema Types.

In-scope variables. This is a set of (expanded QName, type) pairs. 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.

An item is either an atomic value or a node.

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

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

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

A node is an instance of one of the node kinds defined in [XQuery 1.0 and XPath 2.0 Data Model (Second Edition)].

A node test is a condition that must be true for each node selected by a step.

The non-delimiting terminal symbols are: IntegerLiteral, NCName, DecimalLiteral, DoubleLiteral, QName, "ancestor", "ancestor-or-self", "and", "as", "attribute", "cast", "castable", "child", "comment", "descendant", "descendant-or-self", "div", "document-node", "element", "else", "empty-sequence", "eq", "every", "except", "external", "following", "following-sibling", "for", "ge", "gt", "idiv", "if", "in", "instance", "intersect", "is", "item", "le", "lt", "mod", "namespace", "ne", "node", "of", "or", "parent", "preceding", "preceding-sibling", "processing-instruction", "return", "satisfies", "schema-attribute", "schema-element", "self", "some", "text", "then", "to", "treat", "union"

When referring to a type, the term numeric denotes the types xs:integer, xs:decimal, xs:float, and xs:double.

A predicate whose predicate expression returns a numeric type is called a numeric predicate.

For each operator and valid combination of operand types, the operator mapping tables specify a result type and an operator function that implements the semantics of the operator for the given types.

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

A predicate consists of an expression, called a predicate expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others.

Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, 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.

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.

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

A schema type is a type that is (or could be) defined using the facilities of [XML Schema] (including the built-in types of [XML Schema]).

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

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 expression. The term sequence type suggests that this syntax is used to describe the type of an XPath value, which is always a sequence.

Serialization is the process of converting an XDM instance into a sequence of octets (step DM4 in Figure 1.)

A sequence containing exactly one item is called a singleton.

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.

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).

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

A static error is an error that must be detected during the static analysis phase. A syntax error is an example of a static error.

The static type of an expression is a type such that, when the expression is evaluated, the resulting value will always conform to the static type.

A static typing extension is an implementation-defined type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics (Second Edition)].

The Static Typing Feature is an optional feature of XPath that provides support for the static semantics defined in [XQuery 1.0 and XPath 2.0 Formal Semantics (Second Edition)], and requires implementations to detect and report type errors during the static analysis phase.

Statically known collections. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of nodes that would result from calling the fn:collection function with this URI as its argument.

Statically known documents. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument.

Statically known collations. This is an implementation-defined set of (URI, collation) pairs. It defines the names of the collations that are available for use in processing expressions.

Statically known default collection type. This is the type of the sequence of nodes that would result from calling the fn:collection function with no arguments.

Statically known namespaces. This is a set of (prefix, URI) pairs that define all the namespaces that are known during static processing of a given expression.

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 filter expression.

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

Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. 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.

The use of a value whose dynamic type is derived from an expected type is known as subtype substitution.

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

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 /* xgs: xml-version */ annotation.

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.

Each element node and attribute node in an XDM instance has a type annotation (referred to in [XQuery 1.0 and XPath 2.0 Data Model (Second Edition)] as its type-name property.) The type annotation of a node is a schema type that describes the relationship between the string value of the node and its typed value.

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.

Under certain circumstances, an atomic value can be promoted from one type to another. Type promotion is used in evaluating function calls (see 3.1.5 Function Calls) and operators that accept numeric or string operands (see B.2 Operator Mapping).

The typed value of a node is a sequence of atomic values and can be extracted by applying the fn:data function to the node.

In certain situations a value is said to be undefined (for example, the value of the context item, or the typed value of an element node). This term indicates that the property in question has no value and that any attempt to use its value results in an error.

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

A variable reference is a QName preceded by a $-sign.

Variable values. This is a set of (expanded QName, value) pairs. 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.

In addition to static errors, dynamic errors, and type errors, an XPath 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.

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

xs:anyAtomicType is an atomic type that includes all atomic values (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 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: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 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 is derived by restriction from xs:duration. The lexical representation of xs:yearMonthDuration is restricted to contain only year and month components.