XPath语法产生式

[1]	LocationPath	::=	RelativeLocationPath
			| AbsoluteLocationPath
[2]	AbsoluteLocationPath	::=	'/' RelativeLocationPath?
			| AbbreviatedAbsoluteLocationPath
[3]	RelativeLocationPath	::=	Step
			| RelativeLocationPath '/' Step
			| AbbreviatedRelativeLocationPath
[4]	Step	::=	AxisSpecifier NodeTest Predicate*
			| AbbreviatedStep
[5]	AxisSpecifier	::=	AxisName '::'
			| AbbreviatedAxisSpecifier
[6]	AxisName	::=	'ancestor'
			| 'ancestor-or-self'
			| 'attribute'
			| 'child'
			| 'descendant'
			| 'descendant-or-self'
			| 'following'
			| 'following-sibling'
			| 'namespace'
			| 'parent'
			| 'preceding'
			| 'preceding-sibling'
			| 'self'
[7]	NodeTest	::=	NameTest
			| NodeType '(' ')'
			| 'processing-instruction' '(' Literal ')'
[8]	Predicate	::=	'[' PredicateExpr ']'
[9]	PredicateExpr	::=	Expr
[10]	AbbreviatedAbsoluteLocationPath	::=	'//' RelativeLocationPath
[11]	AbbreviatedRelativeLocationPath	::=	RelativeLocationPath '//' Step
[12]	AbbreviatedStep	::=	'.'
			| '..'
[13]	AbbreviatedAxisSpecifier	::=	'@'?
[14]	Expr	::=	OrExpr
[15]	PrimaryExpr	::=	VariableReference
			| '(' Expr ')'
			| Literal
			| Number
			| FunctionCall
[16]	FunctionCall	::=	FunctionName '(' ( Argument ( ',' Argument )* )? ')'
[17]	Argument	::=	Expr
[18]	UnionExpr	::=	PathExpr
			| UnionExpr '|' PathExpr
[19]	PathExpr	::=	LocationPath
			| FilterExpr
			| FilterExpr '/' RelativeLocationPath
			| FilterExpr '//' RelativeLocationPath
[20]	FilterExpr	::=	PrimaryExpr
			| FilterExpr Predicate
[21]	OrExpr	::=	AndExpr
			| OrExpr 'or' AndExpr
[22]	AndExpr	::=	EqualityExpr
			| AndExpr 'and' EqualityExpr
[23]	EqualityExpr	::=	RelationalExpr
			| EqualityExpr '=' RelationalExpr
			| EqualityExpr '!=' RelationalExpr
[24]	RelationalExpr	::=	AdditiveExpr
			| RelationalExpr '<' AdditiveExpr
			| RelationalExpr '>' AdditiveExpr
			| RelationalExpr '<=' AdditiveExpr
			| RelationalExpr '>=' AdditiveExpr
[25]	AdditiveExpr	::=	MultiplicativeExpr
			| AdditiveExpr '+' MultiplicativeExpr
			| AdditiveExpr '-' MultiplicativeExpr
[26]	MultiplicativeExpr	::=	UnaryExpr
			| MultiplicativeExpr MultiplyOperator UnaryExpr
			| MultiplicativeExpr 'div' UnaryExpr
			| MultiplicativeExpr 'mod' UnaryExpr
[27]	UnaryExpr	::=	UnionExpr
			| '-' UnaryExpr
[28]	ExprToken	::=	'(' | ')' | '[' | ']' | '.' | '..' | '@' | ',' | '::'
			| NameTest
			| NodeType
			| Operator
			| FunctionName
			| AxisName
			| Literal
			| Number
			| VariableReference
[29]	Literal	::=	'"' [^"]* '"'
			| "'" [^']* "'"
[30]	Number	::=	Digits ('.' Digits?)?
			| '.' Digits
[31]	Digits	::=	[0-9]+
[32]	Operator	::=	OperatorName
			| MultiplyOperator
			| '/' | '//' | '|' | '+' | '-' | '=' | '!=' | '<' | '<=' | '>' | '>='
[33]	OperatorName	::=	'and' | 'or' | 'mod' | 'div'
[34]	MultiplyOperator	::=	'*'
[35]	FunctionName	::=	QName - NodeType
[36]	VariableReference	::=	'$' QName
[37]	NameTest	::=	'*'
			| NCName ':' '*'
			| QName
[38]	NodeType	::=	'comment'
			| 'text'
			| 'processing-instruction'
			| 'node'
[39]	ExprWhitespace	::=	S