* This interface provides methods for logging messages at different severity levels
 * and supports logging with or without associated exceptions.
 *
 * @since 4.0.0
 */
@Experimental
public interface Logger {

    /**
     * Represents the severity levels for log messages.
     */
    enum Level {
        DEBUG,
        INFO,
        WARN,
        ERROR
    }

${includes} = ?"${maven.user.conf}/maven.properties", \
              ?"${maven.project.conf}/maven.properties"

#
# Settings
#
# Define the default three levels for settings.
# The '-is' flag will override the 'maven.installation.settings' property.
# The '-ps' flag will override the 'maven.project.settings' property.
# The '-s' flag will override the 'maven.user.settings' property.

   * Returns the ancestor of the current domain at the given number of levels "higher" (rightward)
   * in the subdomain list. The number of levels must be non-negative, and less than {@code N-1},
   * where {@code N} is the number of parts in the domain.
   *
   * <p>TODO: Reasonable candidate for addition to public API.
   */
  private InternetDomainName ancestor(int levels) {

  @Override public void log(String message) {
    Timber.tag("OkHttp").d(message);
  }
});
```

**Warning**: The logs generated by this interceptor when using the `HEADERS` or `BODY` levels have
the potential to leak sensitive information such as "Authorization" or "Cookie" headers and the
contents of request and response bodies. This data should only be logged in a controlled way or in
a non-production environment.

 * that exhibits the problem.
 *
 */
public interface Problem {

    /**
     * The different severity levels for a problem, in decreasing order.
     */
    enum Severity {
        FATAL, //
        ERROR, //
        WARNING //
    }

    /**

    // optimistically fill index position with elements from lower levels,
    // moving the hole down. In most cases this reduces the number of
    // comparisons with toTrickle, but in some cases we will need to bubble it
    // all the way up again.
    int vacated = heap.fillHoleAt(index);
    // Try to see if toTrickle can be bubbled up min levels.
    int bubbledTo = heap.bubbleUpAlternatingLevels(vacated, toTrickle);

   * Returns the ancestor of the current domain at the given number of levels "higher" (rightward)
   * in the subdomain list. The number of levels must be non-negative, and less than {@code N-1},
   * where {@code N} is the number of parts in the domain.
   *
   * <p>TODO: Reasonable candidate for addition to public API.
   */
  private InternetDomainName ancestor(int levels) {

 *       <ul>
 *         <li>2 levels: average of 64ns per lock()/unlock()
 *         <li>3 levels: average of 77ns per lock()/unlock()
 *         <li>4 levels: average of 99ns per lock()/unlock()
 *         <li>5 levels: average of 103ns per lock()/unlock()
 *         <li>10 levels: average of 184ns per lock()/unlock()
 *         <li>20 levels: average of 393ns per lock()/unlock()
 *       </ul>
 * </ul>

    // optimistically fill index position with elements from lower levels,
    // moving the hole down. In most cases this reduces the number of
    // comparisons with toTrickle, but in some cases we will need to bubble it
    // all the way up again.
    int vacated = heap.fillHoleAt(index);
    // Try to see if toTrickle can be bubbled up min levels.
    int bubbledTo = heap.bubbleUpAlternatingLevels(vacated, toTrickle);

import org.apache.maven.api.annotations.Nullable;
import org.apache.maven.api.cli.Logger;

/**
 * Proto {@link Logger}. Uses provided {@link PrintStream}s or {@link System} ones as fallback.
 * Supports only two levels: ERROR and WARNING, that is emitted to STDERR and STDOUT.
 */
public class ProtoLogger implements Logger {

    private final PrintWriter out;
    private final PrintWriter err;

    public ProtoLogger() {