Add XPath 1.0 grammar.

docs/xpath.rst

+=================
+XPath Expressions
+=================
+
+.. productionlist::
+   LocationPath: `RelativeLocationPath` | `AbsoluteLocationPath`
+   AbsoluteLocationPath: "/" `RelativeLocationPath`?
+                       : | `AbbreviatedAbsoluteLocationPath`
+   RelativeLocationPath: `Step`
+                       : | `RelativeLocationPath` "/" `Step`
+		       : `AbbreviatedRelativeLocationPath`
+   Step: `AxisSpecifier` `NodeTest` `Predicate`*
+       : | `AbbreviatedStep`
+   AxisSpecifier: `AxisName` "::"
+                : `AbbreviatedAxisSpecifier`
+   AxisName: "ancestor"
+           : | "ancestor-or-self"
+	   : | "attribute"
+	   : | "child"
+	   : | "descendant"
+	   : | "descendant-or-self"
+	   : | "following"
+	   : | "following-sibling"
+	   : | "namespace"
+	   : | "parent"
+	   : | "preceding"
+	   : | "preceding-sibling"
+	   : | "self"
+   NodeTest: `NameTest`
+           : | `NodeType` "(" ")"
+	   : | "processing-instruction" "(" `Literal` ")"
+   Predicate: "[" `PredicateExpr` "]"
+   PredicateExpr: `Expr`
+   AbbreviatedAbsoluteLocationPath: "//" `RelativeLocationPath`
+   AbbreviatedRelativeLocationPath: `RelativeLocationPath` "//" `Step`
+   AbbreviatedStep: "." | ".."
+   AbbreviatedAxisSpecifier: "@"?
+   Expr: `OrExpr`
+   PrimaryExpr: `VariableReference`
+              : | "(" `Expr` ")"
+	      : | `Literal`
+	      : | `Number`
+	      : | `FunctionCall`
+   FunctionCall: `FunctionName` "(" (`Argument` ("," `Argument`)*)? ")"
+   Argument: `Expr`
+   UnionExpr: `PathExpr`
+            : | `UnionExpr` "|" `PathExpr`
+   PathExpr: `LocationPath`
+           : | `FilterExpr`
+	   : | `FilterExpr` "/" `RelativeLocationPath`
+	   : | `FilterExpr` "//" `RelativeLocationPath`
+   FilterExpr: `PrimaryExpr`
+             : | `FilterExpr` `Predicate`
+   OrExpr: `AndExpr`
+         : | `OrExpr` "or" `AndExpr`
+   AndExpr: `EqualityExpr`
+          : | `AndExpr` "and" `EqualityExpr`
+   EqualityExpr: `RelationalExpr`
+               : | `EqualityExpr` "=" `RelationalExpr`
+               : | `EqualityExpr` "!=" `RelationalExpr`
+   RelationalExpr: `AdditiveExpr`
+                 : | `RelationalExpr` "<" `AdditiveExpr`
+                 : | `RelationalExpr` ">" `AdditiveExpr`
+                 : | `RelationalExpr` "<=" `AdditiveExpr`
+                 : | `RelationalExpr` ">=" `AdditiveExpr`
+   AdditiveExpr: `MultiplicativeExpr`
+               : `AdditiveExpr` "+" `MultiplicativeExpr`
+               : `AdditiveExpr` "-" `MultiplicativeExpr`
+   MultiplicativeExpr: `UnaryExpr`
+                     : | `MultiplicativeExpr` `MultiplyOperator` `UnaryExpr`
+                     : | `MultiplicativeExpr` "div" `UnaryExpr`
+                     : | `MultiplicativeExpr` "mod" `UnaryExpr`
+   UnaryExpr: `UnionExpr`
+            : "-" `UnaryExpr`
+   ExprToken: "(" | ")" | "[" | "]" | "." | ".."
+            :| "@" | "," | "::"
+            : | `NameTest`
+	    : | `NodeType`
+	    : | `Operator`
+	    : | `FunctionName`
+	    : | `AxisName`
+	    : | `Literal`
+	    : | `Number`
+	    : | `VariableReference`
+   Literal: '"' [^"]* '"'
+          : | "'" [^']* "'"
+   Number: `Digits` ("." `Digits`?)?
+         : | "." `Digits`
+   Digits: [0-9]+
+   Operator: `OperatorName`
+           : | `MultiplyOperator`
+	   : | "/" | "//" | "|" | "+" | "-" | "="
+	   : | "!=" | "<" | "<=" | ">" | ">="
+   OperatorName: "and" | "or" | "mod" | "div"
+   MultiplyOperator: "*"
+   FunctionaName: `QName` - `NodeType`
+   VariableReference: "$" `QName`
+   NameTest: "*"
+           : | `NCName` ":" "*"
+	   : | `QName`
+   NodeType: "comment"
+           : | "text"
+	   : | "processing-instruction"
+	   : | "node"
+   ExprWhitespace: `S`
+   S: (#x20 | #x9 | #xD | #xA)+
+   QName: `PrefixedName`
+        : | `UnprefixedName`
+   PrefixedName: `Prefix` ":" `LocalPart`
+   UnprefixedName: `LocalPart`
+   Prefix: `NCName`
+   LocalPart: `NCName`
+   NCName: `Name` - (`Char`* ":" `Char`*)
+   Name: `NameStartChar` `NameChar`*
+   NameStartChar: ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6]
+                : | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D]
+		: | [#x37F-#x1FFF] | [#x200C-#x200D]
+		: | [#x2070-#x218F] | [#x2C00-#x2FEF]
+		: | [#x3001-#xD7FF] | [#xF900-#xFDCF]
+		: | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
+   NameChar: `NameStartChar` | "-" | "." | [0-9] | #xB7
+           : | [#x0300-#x036F] | [#x203F-#x2040]
+   Char: #x9 | #xA | #xD | [#x20-#xD7FF]
+       : | [#xE000-#xFFFD] | [#x10000-#x10FFFF]