.collect(toSet());
    }

    /**
     * @return Required active profile identifiers, never {@code null}.
     */
    public Set<String> getRequiredActiveProfileIds() {
        return getProfileIds(pa -> !pa.optional && pa.active);
    }

    /**
     * @return Optional active profile identifiers, never {@code null}.
     */
    public Set<String> getOptionalActiveProfileIds() {

    /**
     * Gets the identifiers of those profiles that should be activated by explicit demand.
     *
     * @return The identifiers of those profiles to activate, never {@code null}.
     */
    List<String> getActiveProfileIds();

    /**
     * Gets the identifiers of those profiles that should be deactivated by explicit demand.
     *
     * @return The identifiers of those profiles to deactivate, never {@code null}.

    @Override
    public List<String> getActiveProfileIds() {
        return activeProfileIds;
    }

    /**
     * Sets the identifiers of those profiles that should be activated by explicit demand.
     *
     * @param activeProfileIds The identifiers of those profiles to activate, may be {@code null}.
     * @return This context, never {@code null}.
     */

    /**
     * Gets the sequence of model identifiers that denote the lineage of models from which the effective model was
     * constructed. Model identifiers should be handled as "opaque strings" and this method should be used as source
     * if navigating the linage. The first identifier from the list denotes the model on which the model builder
     * was originally invoked. The last identifier will always be the super POM.
     *

    ModelBuildingRequest setProfiles(List<Profile> profiles);

    /**
     * Gets the identifiers of those profiles that should be activated by explicit demand.
     *
     * @return The identifiers of those profiles to activate, never {@code null}.
     */
    List<String> getActiveProfileIds();

    /**
     * Sets the identifiers of those profiles that should be activated by explicit demand.
     *

          MethodIdentifier ident = new MethodIdentifier(method);
          if (!identifiers.containsKey(ident)) {
            identifiers.put(ident, method);
          }
        }
      }
    }
    return ImmutableList.copyOf(identifiers.values());
  }

  /** Global cache of classes to their flattened hierarchy of supertypes. */

   |
   | Default: false
  <offline>false</offline>
  -->

  <!-- pluginGroups
   | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.
   | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers
   | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.
   |-->
  <pluginGroups>

     * @see DependencyCoordinates#getOptional()
     */
    boolean isOptional();

    /**
     * {@return coordinates with the same identifiers as this dependency}
     */
    @Nonnull
    @Override
    DependencyCoordinates toCoordinates();

 * </p>
 *
 * @since 4.0.0
 */
@Experimental
@Immutable
public interface Artifact {
    /**
     * {@return a unique identifier for this artifact}
     * The identifier is composed of groupId, artifactId, extension, classifier, and version.
     *
     * @see ArtifactCoordinates#getId()
     */
    @Nonnull
    default String key() {

using these rules.
</p>


<h3 id="Identifiers">Identifiers</h3>

<p>
Identifiers name program entities such as variables and types.
An identifier is a sequence of one or more letters and digits.
The first character in an identifier must be a letter.
</p>
<pre class="ebnf">
identifier = letter { letter | unicode_digit } .
</pre>
<pre>
a
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