* @return the user settings source or {@code null} if none
     */
    @Nonnull
    Optional<Source> getUserSettingsSource();

    /**
     * The optional interpolation source used for interpolation.
     *
     * @return the interpolation source for interpolation
     */
    @Nonnull
    Optional<UnaryOperator<String>> getInterpolationSource();

    @Nonnull
    static SettingsBuilderRequest build(

    /**
     * Gets the system properties to use for interpolation. The system properties are collected from the runtime
     * environment like {@link System#getProperties()} and environment variables.
     *
     * @return The system properties, never {@code null}.
     */
    Properties getSystemProperties();

    /**
     * Sets the system properties to use for interpolation. The system properties are collected from the runtime

        return this;
    }

    @Override
    public Map<String, String> getSystemProperties() {
        return systemProperties;
    }

    /**
     * Sets the system properties to use for interpolation and profile activation. The system properties are collected
     * from the runtime environment like {@link System#getProperties()} and environment variables.
     *

import org.codehaus.plexus.interpolation.AbstractValueSource;
import org.codehaus.plexus.interpolation.InterpolationPostProcessor;
import org.codehaus.plexus.interpolation.MapBasedValueSource;
import org.codehaus.plexus.interpolation.ObjectBasedValueSource;
import org.codehaus.plexus.interpolation.PrefixAwareRecursionInterceptor;
import org.codehaus.plexus.interpolation.PrefixedObjectValueSource;

public interface ModelValidator {

    /**
     * Checks the specified (raw) model for missing or invalid values. The raw model is directly created from the POM
     * file and has not been subjected to inheritance, interpolation or profile/default injection.
     *
     * @param model The model to validate, must not be {@code null}.
     * @param request The model building request that holds further settings, must not be {@code null}.

     * Gets the system properties to use for interpolation and profile activation. The system properties are collected
     * from the runtime environment like {@link System#getProperties()} and environment variables.
     *
     * @return The execution properties, never {@code null}.
     */
    Map<String, String> getSystemProperties();

    /**

     * Returns immutable user properties to use for interpolation. The user properties have been configured directly
     * by the user, e.g. via the {@code -Dkey=value} parameter on the command line.
     *
     * @return the user properties, never {@code null}
     */
    @Nonnull
    Map<String, String> getUserProperties();

    /**
     * Returns immutable system properties to use for interpolation. The system properties are collected from the

     *
     * @return The raw model, never {@code null}.
     */
    Model getRawModel();

    /**
     * Gets the specified raw model as it was read from a model source. Apart from basic validation, a raw model has not
     * undergone any updates by the model builder, e.g. reflects neither inheritance nor interpolation. The model

    <contributor>
      <name>Thomas Meyer</name>
    </contributor>
  </contributors>

  <dependencies>
    <dependency>
      <groupId>org.codehaus.plexus</groupId>
      <artifactId>plexus-interpolation</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-api-settings</artifactId>
    </dependency>
    <dependency>

     *
     * @return the file model, never {@code null}.
     */
    @Nonnull
    Model getFileModel();

    /**
     * Gets the file model + build pom transformation, without inheritance nor interpolation.
     *
     * @return The raw model, never {@code null}.
     */
    @Nonnull
    Model getRawModel();

    /**
     * Gets the effective model of the parent POM.
     *