Syntax Productions

These rules mainly use familiar notations: «* » for repetition, parentheses for grouping, «? » to indicate that the preceding construct is optional, and « » to separate alternatives.

Simple tokens are represented using chevrons, for example «, » in the first rule represents a literal comma.

Sometimes multiple tokens are grouped inside a pair of chevrons, for example «for $ » in the third rule. This notation indicates that there are two tokens (whitespace may appear between them) but that the parser needs to recognize both tokens together in order to proceed. The keyword «for » on its own is not enough to recognize a ForExpr, because it might equally well be an element name appearing as a step in a path expression: the parser is therefore looking for the composite symbol consisting of the token «for » followed by the token «$ ».

Whitespace is always allowed between two tokens, whether these are grouped using chevrons or not. Whitespace is generally required between two tokens in cases where the first character of the second token could otherwise be taken as a continuation of the first token: for example, in the expression «$a - $b » whitespace is required before the «- » (but not after it). There are some exceptions to this rule: for example, whitespace is not required (but is allowed) before the «:: » that follows an axis name.

The rules as I have given them here do not correspond exactly with the rules as given in the W3C XPath specification. I have divided some rules and merged others for clarity, to correspond with the way the semantics are presented in XPath 2.0 Programmer's Reference. The W3C rules are sometimes distorted by the need to achieve a grammar that is provably nonambiguous, and also by the need to reuse syntactic elements between the XPath and XQuery specifications. I don't have these constraints here, so I can make it more user -friendly.

Symbol	Syntax
Expr	ExprSingle (, ExprSingle) *
ExprSingle	ForExpr QuantifiedExpr If Expr OrExpr
ForExpr	for $ VarName in ExprSingle (, $ VarName in ExprSingle)* return ExprSingle
QuantifiedExpr	(some $ every $) VarName in ExprSingle (, $ VarName in ExprSingle)* satisfies ExprSingle
If Expr	if (Expr) then ExprSingle else ExprSingle
OrExpr	AndExpr (or AndExpr)*
AndExpr	ComparisonExpr (and ComparisonExpr)*
ComparisonExpr	RangeExpr (ValueComp GeneralComp NodeComp) RangeExpr)?
ValueComp	eq ne lt le gt ge
GeneralComp	= != < <= > >=
NodeComp	is << >>
RangeExpr	AdditiveExpr (to AdditiveExpr)?
AdditiveExpr	MultiplicativeExpr ((+)-) MultiplicativeExpr)*
MultiplicativeExpr	UnionExpr ((* div idiv mod) UnionExpr)*
UnionExpr	IntersectExceptExpr ((union ) IntersectExceptExpr)*
IntersectExceptExpr	InstanceOfExpr ((intersect except) InstanceOfExpr)*
InstanceofExpr	TreatExpr (instance of SequenceType)?
TreatExpr	CastableExpr (treat as SequenceType)?
CastableExpr	CastExpr (castable as SingleType)?
CastExpr	UnaryExpr (cast as SingleType)?
UnaryExpr	(+-)* PathExpr
PathExpr	(/ RelativePathExpr?) (// RelativePathExpr) RelativePathExpr
RelativePathExpr	StepExpr ((/ //) StepExpr)*
StepExpr	AxisStep FilterExpr
AxisStep	(ForwardStep ReverseStep) PredicateList
FilterExpr	PrimaryExpr PredicateList
PredicateList	Predicate *
Predicate	[ Expr ]
PrimaryExpr	Literal VarRef ParenthesizedExpr ContextItemExpr FunctionCall
Literal	NumericLiteral StringLiteral
NumericLiteral	IntegerLiteral DecimalLiteral DoubleLiteral
VarRef	$ VarName
Parenthesized Expr	(Expr?)
ContextItemExpr	.
FunctionCall	FunctionName ((ExprSingle (, ExprSingle)*)?)
FunctionName	QName
ForwardStep	(ForwardAxis NodeTest) AbbrevForwardStep
ReverseStep	(ReverseAxis NodeTest) AbbrevReverseStep
Abbrev ForwardStep	@? NodeTest
Abbrev ReverseStep	..
ForwardAxis	child:: descendant :: attribute:: self :: descendant-or-self :: following-sibling :: following :: namespace ::
ReverseAxis	parent :: ancestor :: preceding-sibling :: preceding :: ancestor-or-self ::
NodeTest	KindTest NameTest
NameTest	QName Wildcard
SingleType	AtomicType ??
SequenceType	(ItemType OccurrenceIndicator?) empty ()
AtomicType	QName
ItemType	AtomicType KindTest item ()
Occurrence Indicator	? * +
KindTest	DocumentTest ElementTest AttributeTest PITest CommentTest TextTest AnyKindTest
ElementTest	BasicElementTest SchemaElementTest
AttributeTest	BasicAttributeTest SchemaAttributeTest
Basic ElementTest	element ((ElementNameOrWildCard (, TypeName ??)?)?)
Basic AttributeTest	attribute ((AttributeNameOrWildcard (, TypeName)?)?)
ElementName OrWildcard	ElementName *
AttributeName OrWildcard	AttributeName *
ElementName	QName
AttributeName	QName
TypeName	QName
Schema ElementTest	schema-element (ElementName)
Schema AttributeTest	schema-attribute (AttributeName)
PITest	processing-instruction ((NCName StringLiteral) ?)
DocumentTest	document-node (ElementTest?)
CommentTest	comment ()
TextTest	text ()
AnyKindTest	node ()