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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
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 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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/** 
 * Core classes of the flexible query parser framework.
 *
 * <h2>Flexible Query Parser</h2>
 * 
 * <p>
 * This package contains the necessary classes to implement a query parser.  
 * 
 * <p>
 * A query parser is divided in at least 2 phases, text parsing and query building, and one optional phase called query processing.
 * 
 * <h3>First Phase: Text Parsing</h3>
 * <p>
 * The text parsing phase is performed by a text parser, which implements {@link org.apache.lucene.queryparser.flexible.core.parser.SyntaxParser} interface.
 * A text parser is responsible to get a query string and convert it to a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree,
 * which is an object structure that represents the elements defined in the query string.
 * 
 * <h3>Second (optional) Phase: Query Processing</h3>
 * <p>
 * The query processing phase is performed by a query processor, which implements {@link org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessor}.
 * A query processor is responsible to perform any processing on a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree. This phase
 * is optional and is used only if an extra processing, validation, query expansion, etc needs to be performed in a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree.
 * The {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree can be either be generated by a text parser or programmatically created.
 * 
 * <h3>Third Phase: Query Building</h3>
 * <p>
 * The query building phase is performed by a query builder, which implements {@link org.apache.lucene.queryparser.flexible.core.builders.QueryBuilder}.
 * A query builder is responsible to convert a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree into an arbitrary object, which
 * is usually used to be executed against a search index.   
 */
package org.apache.lucene.queryparser.flexible.core;
