Core classes of the flexible query parser framework.

## Flexible Query Parser

This package contains the necessary classes to implement a query parser.

A query parser is divided in at least 2 phases, text parsing and query building, and one optional phase called query processing.

### First Phase: Text Parsing

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.

### Second (optional) Phase: Query Processing

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.

### Third Phase: Query Building

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.