Interfaces and implementations used by query node processors

## Query Node Processors

The package `org.apache.lucene.queryParser.processors` contains interfaces that should be implemented by every query node processor.

The interface that every query node processor should implement is {@link org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessor}.

A query node processor should be used to process a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree. {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} trees can be programmatically created or generated by a text parser. See {@link org.apache.lucene.queryparser.flexible.core.parser} for more details about text parsers.

A query node processor should be used to process a {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} tree. {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode} trees can be programmatically created or generated by a text parser. See {@link org.apache.lucene.queryparser.flexible.core.parser} for more details about text parsers.

A pipeline of processors can be assembled using {@link org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessorPipeline}.

Implementors may want to extend {@link org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessorImpl}, which simplifies the implementation, because it walks automatically the {@link org.apache.lucene.queryparser.flexible.core.nodes.QueryNode}. See {@link org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessorImpl} for more details.