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// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
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/**
* This package provides classes associated with XPath expression handling. Generally, these
* classes are not intended to be used directly by user-written applications; the API for XPath
* evaluation is now provided by classes in the package net.sf.saxon.xpath
* The principal classes are:
* Expression:
* This represents an XPath Expression. There is a static method Expression.make() which is
* used to construct an Expression from a String (it is a factory method rather than a
* constructor, because it typically returns some subclass of Expression according
* to the syntax supplied). Subclasses of Expression represent different kinds of expression
* such as StringExpression and BooleanExpression. What they all have in common is an evaluate()
* method, which evaluates the expression in a given context to yield a Value, and an iterate() method,
* which treats the result of the expression as a sequence, and iterates over the items in the sequence.
* ExpressionParser:
* This class does the work of parsing both Expressions and Patterns. Applications should not call
* it directly. It uses the class Tokenizer for lexical analysis.
* StaticContext:
* This interface defines the information available at the time an expression is being parsed. This
* includes the names of variables, the bindings of namespace prefixes, the functions that are available,
* the names of collating sequences, and so on. When an XPath expression appears in a stylesheet, the
* class net.sf.saxon.style.ExpressionContext provides the StaticContext. For a free-standing XPath
* expression, the class net.sf.saxon.xpath.StandaloneContext is available, though a user-written
* class that implements StaticContext can also be used.
* XPathContext:
* This class defines the context information available at run-time, for example the context node, position,
* and size. (It actually does this by wrapping a SequenceIterator that represents the current sequence.)
* When expressions are used during an XSLT transformation, the XPathContext also provides access to the
* Controller, which contains all the context information about XSLT processing (for example the current template,
* the current group, and so on).
* Most of the classes in this package represent individual syntactic constructs found in XPath or XQuery expressions:
* for example ValueComparison, UserFunctionCall, and RootExpression. The
* objects
* that instantiate these classes form the nodes on the Abstract Syntax Tree constructed by the compiler and modified
* by the optimizer; at run-time their methods are used to drive a pipelined evaluation of the expression.
* The distinction between the compiled form of XSLT instructions and the compiled form of XPath expressions has
* become blurred. Generally, the compiled form of instructions is in the package net.sf.saxon.instruct
* (this includes expressions in XQuery that are equivalent to XSLT instructions, for example element constructors).
* However, some constructs such as conditional expressions now exist in both languages and may generate the same
* run-time constructs.
*/
package net.sf.saxon.expr;