import java.io.*;
import java.util.*;

public interface Handler {
  /**
   * Returns the extension for the files about which we know.
   *
   * @return the extension for the files about which we know
   */
  List<String> extensions();

  /**
   * Returns explanation of handler.
   *
   * @return explanation of handler
   */
  String description();
  
  /**
   * Returns the key-value pairs for the explanation of the file we use.
   *
   * @returns the key-value pairs for the explanation of the file we use
   */
  Map<String,String> explain(File f);
  
  /**
   * Returns list of keys to use in explanation.  We want these ordered.
   *
   * @return list of keys to use in explanation
   */
  List<String> keys();
}