*
     * @return the message describing this problem, never {@code null}
     */
    @Nonnull
    String getMessage();

    /**
     * Gets the severity level of this problem.
     *
     * @return the severity level of this problem, never {@code null}
     */
    @Nonnull
    Severity getSeverity();

    /**
     * The different severity levels for a problem, in decreasing order.
     *

     * @param dir the directory to locate the pom for, never {@code null}
     * @return a {@code Source} pointing to the located pom or an empty {@code Optional} if none was found by this parser
     */
    @Nonnull
    Optional<Source> locate(@Nonnull Path dir);

    /**
     * Parse the model obtained previously by a previous call to {@link #locate(Path)}.
     *
     * @param source the source to parse, never {@code null}

     *
     * @param model the input model
     * @return the transformed model, or the input model if no transformation is needed
     * @throws ModelTransformerException
     */
    @Nonnull
    default Model transformFileModel(@Nonnull Model model) throws ModelTransformerException {
        return model;
    }

    /**
     * Apply a transformation on the raw models.
     *

     * @return the phase
     */
    @Nonnull
    String phase() default "";

    /**
     * Goal to fork. Note that specifying a phase overrides specifying a goal. The specified <code>goal</code> must be
     * another goal of the same plugin.
     * @return the goal
     */
    @Nonnull
    String goal() default "";

    /**

     */
    @Nonnull
    List<Exception> getExceptions();

    /**
     * Gets the versions (in ascending order) that matched the requested range.
     *
     * @return The list of matching versions, never {@code null}. An empty list indicates
     *         no versions matched the requested range.
     */
    @Nonnull
    List<Version> getVersions();

    /**

     * a <abbr>JAR</abbr> containing test classes, a POM file, <i>etc.</i>
     */
    @Nonnull
    Type getType();

    /**
     * {@return the time at which the dependency will be used}
     * It may be, for example, at compile time only, at run time, or at test time.
     */
    @Nonnull
    DependencyScope getScope();

    /**

     * create a custom {@code Type} for it.
     *
     * @param id the id of the type to retrieve
     * @return the type
     */
    @Nonnull
    @Override
    default Type require(@Nonnull String id) {
        return lookup(id).orElseThrow(() -> new IllegalArgumentException("Unknown extensible enum value '" + id + "'"));
    }

     * @return an identification of the patch-module path for the given module.
     *
     * @see Modular#moduleName()
     */
    @Nonnull
    public static Modular patchModule(@Nonnull String moduleName) {
        return PATCH_MODULE.new Modular(moduleName);
    }

    /**

      Class<? super @NonNull E> type, E... contents) {
    return new MinimalCollection<>(type, true, contents);
  }

  private final E[] contents;
  private final Class<? super @NonNull E> type;
  private final boolean allowNulls;

  // Package-private so that it can be extended.
  MinimalCollection(Class<? super @NonNull E> type, boolean allowNulls, E... contents) {

     * @throws DependencyResolverException
     */
    List<Node> flatten(@Nonnull Session session, @Nonnull Node node, @Nullable PathScope scope)
            throws DependencyResolverException;

    @Nonnull
    default DependencyResolverResult flatten(
            @Nonnull Session session, @Nonnull Project project, @Nonnull PathScope scope) {
        return flatten(DependencyResolverRequest.build(