for (Plugin element : tgt) {
                    Object key = getPluginKey().apply(element);
                    Plugin existing = master.get(key);
                    if (existing != null) {
                        element = mergePlugin(element, existing, sourceDominant, context);

                        master.put(key, element);

                        if (!pending.isEmpty()) {

                for (Plugin element : tgt) {
                    Object key = getPluginKey().apply(element);
                    merged.put(key, element);
                }

                Map<Object, Plugin> added = new LinkedHashMap<>();

                for (Plugin element : src) {
                    Object key = getPluginKey().apply(element);
                    Plugin existing = merged.get(key);

        dependencies = new LinkedHashMap<>(count + count / 3);
    }

    /**
     * Adds the given path element to the specified type of path.
     *
     * @param type the type of path (class-path, module-path, …)
     * @param path the path element to add
     */
    private void addPathElement(PathType type, Path path) {

          <artifactId>maven-it-plugin-a</artifactId>
          <version>2.1-SNAPSHOT</version>
          <executions>
            <execution>
              <!-- NOTE: Implicitly reference "default" id here, i.e. omit the <id> element -->
              <phase>parent-default</phase>
            </execution>
            <execution>
              <id>non-default</id>
              <phase>parent-non-default</phase>
            </execution>

        <artifactId>maven-it-plugin-a</artifactId>
        <version>2.1-SNAPSHOT</version>
        <executions>
          <execution>
            <!-- NOTE: Implicitly reference "default" id here, i.e. omit the <id> element -->
            <phase>parent-default</phase>
          </execution>
          <execution>
            <id>non-default</id>
            <phase>parent-non-default</phase>
          </execution>
        </executions>

        } catch (XMLStreamException e) {
            throw new IOException(e.getMessage(), e);
        }

        if (!"extension".equals(dom.getName())) {
            throw new IOException("Unexpected root element \"" + dom.getName() + "\", expected \"extension\"");
        }

        extensionDescriptor.setExportedPackages(parseStrings(dom.getChild("exportedPackages")));

     * The head of returned list is result of {@link Project#getArtifacts()} method, so same applies here: the list can have
     * minimum of one element. The maximum number of elements is in turn dependent on build configuration and lifecycle
     * phase when this method was invoked (i.e. is javadoc jar built and attached, is sources jar built attached, are

   |-->
  <mirrors>
    <!-- mirror
     | Specifies a repository mirror site to use instead of a given repository. The repository that
     | this mirror serves has an ID that matches the mirrorOf element of this mirror. IDs are used
     | for inheritance and direct lookup purposes, and must be unique across the set of mirrors.
     |
    <mirror>
      <id>mirrorId</id>
      <mirrorOf>repositoryId</mirrorOf>

     * If {@code element} is not {@code null}, child configuration element with the specified name will
     * be unmarshalled.
     *
     * @param configuration The configuration to unmarshal, may be {@code null}.
     * @param element Configuration element name to unmarshal or {@code null} to unmarshal entire configuration.

 * The maven super model

 * how parent poms are processed

 * the order in which elements in the POM are overridden

 * minimum element-set for a valid project pom


Maven super model

 Inheritance is recursive in Maven but there is a special model which is the implicit super parent in the lineage
 of models you may specify: