}
                if (selected == null) {
                    selected = type;
                } else if (unknown) {
                    // More than one filtered value, and we don't know how to handle at least one of them.
                    // TODO: add a plugin mechanism for allowing plugin to specify their selection algorithm.
                    return Optional.empty();
                }
            }

 * and semantically represents a known <i>kind</i> of dependency.
 * <p>
 * It provides information about the file type (or extension) of the associated artifact,
 * its default classifier, and how the artifact will be used in the build when creating
 * class-paths or module-paths.
 * <p>
 * For example, the type {@code java-source} has a {@code jar} extension and a

import org.eclipse.aether.repository.RemoteRepository;
import org.slf4j.LoggerFactory;

// TODO the antrun plugin has its own configurator, the only plugin that does. might need to think about how that works
// TODO remove the coreArtifactFilterManager

/**
 * DefaultBuildPluginManager
 */
@Named
@Singleton
public class DefaultBuildPluginManager implements BuildPluginManager {

    public int hashCode() {
        return items.hashCode();
    }

    // CHECKSTYLE_OFF: LineLength

    /**
     * Main to test version parsing and comparison.
     * <p>
     * To check how "1.2.7" compares to "1.2-SNAPSHOT", for example, you can issue
     * <pre>java -jar ${maven.repo.local}/org/apache/maven/maven-artifact/${maven.version}/maven-artifact-${maven.version}.jar "1.2.7" "1.2-SNAPSHOT"</pre>

+-----+
${maven.home}
     |
     +--- maven.properties
+-----+

* Group configuration

 As far as properties go for an entire build the maven.properties could be placed at
 the top of the group but I'm not really sure how this might work. There could probably
 also be a directory for plugins.xml and maven.properties.

* Project configuration

 At the project level all configuration is achieved by tweaking the POM. One of the differences between

import org.apache.maven.plugin.PluginExecutionException;
import org.apache.maven.project.ProjectBuildingException;
import org.apache.maven.project.ProjectBuildingResult;

/*

- test projects for each of these
- how to categorize the problems so that the id of the problem can be match to a page with descriptive help and the test
  project
- nice little sample projects that could be run in the core as well as integration tests

      <artifactId>maven-di</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-model</artifactId>
    </dependency>
    <!-- Remove the following two deps to see how to remove Settings from the core -->
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-settings</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>

implementations. Index The Index contains an alphabetic list of all classes, interfaces, constructors, methods, and fields. Prev/Next These links take you to the next or previous class, interface, package, or related page. Frames/No Frames These links show and hide the HTML frames. All pages are available with or without frames. Serialized Form Each serializable or externalizable class has a description of its serialization fields and methods. This information is of interest to re-implementors, not to...

    //
    // p1 inherits from p0
    // p0 inherits from super model
    //
    // or we can show it graphically as:
    //
    // p1 ---> p0 --> super model
    //
    // ----------------------------------------------------------------------

    /**
     * How the test project is set up:
     *
     * 1. dependencyManagement lists dependencies on a & b,
     *    with an exclusion on c in b.

 * under the License.
 */
package org.apache.maven.artifact.handler;

/**
 * An artifact handler contains information explaining how an artifact plugs into the Maven build:<ul>
 * <li>Information needed to find the artifact file in a repository including extension and classifier</li>
 * <li>Information on how to use the artifact as a dependency: whether to add it to the classpath, whether to load its
 * dependencies transitively</li>
 * </ul>
 *