### Technical Details: `root_path` { #technical-details-root-path }

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

/**
 * Pluggable interface for compiling a regex pattern. By default this package uses the {@code
 * java.util.regex} library, but an alternate implementation can be supplied using the {@link
 * java.util.ServiceLoader} mechanism.
 */
@GwtIncompatible
interface PatternCompiler {
  /**
   * Compiles the given pattern.
   *
   * @throws IllegalArgumentException if the pattern is invalid
   */
  @RestrictedApi(

/**
 * Pluggable interface for compiling a regex pattern. By default this package uses the {@code
 * java.util.regex} library, but an alternate implementation can be supplied using the {@link
 * java.util.ServiceLoader} mechanism.
 */
@GwtIncompatible
interface PatternCompiler {
  /**
   * Compiles the given pattern.
   *
   * @throws IllegalArgumentException if the pattern is invalid
   */
  @RestrictedApi(

 */
public interface ScriptEngine {

    /**
     * Evaluates a template string with the provided parameter map.
     * The template is processed using the script engine's templating mechanism,
     * with parameters from the paramMap substituted into the template.
     *
     * @param template the template string to evaluate
     * @param paramMap the map of parameters to substitute into the template

 * beyond the standard ones provided by Maven (like jar, war, ear, etc.). Implementations of this
 * interface will be discovered through the Java ServiceLoader mechanism and their provided
 * packaging types will be available throughout the Maven build process.
 * <p>
 * Example usage:
 * <pre>
 * public class CustomPackagingProvider implements PackagingProvider {

 * <p>
 * This interface serves as the base for all Service Provider Interface (SPI) components in Maven.
 * Classes implementing this interface can be discovered and loaded by Maven through the
 * Java ServiceLoader mechanism, allowing plugins and extensions to contribute functionality
 * to the Maven build process.
 * <p>
 * SPI services are typically registered in {@code META-INF/services/} files corresponding to

 * of phases that can be executed during a build.
 * <p>
 * Implementations of this interface will be discovered through the Java ServiceLoader mechanism
 * and their provided lifecycles will be available throughout the Maven build process.
 * <p>
 * Example usage:
 * <pre>
 * public class CustomLifecycleProvider implements LifecycleProvider {

 * in different contexts, such as compilation, testing, or runtime.
 * <p>
 * Implementations of this interface will be discovered through the Java ServiceLoader mechanism
 * and their provided path scopes will be available throughout the Maven build process.
 * <p>
 * Example usage:
 * <pre>
 * public class CustomPathScopeProvider implements PathScopeProvider {

 * are handled, including their default extension, classifier, and language.
 * <p>
 * Implementations of this interface will be discovered through the Java ServiceLoader mechanism
 * and their provided types will be available throughout the Maven build process.
 * <p>
 * Example usage:
 * <pre>
 * public class CustomTypeProvider implements TypeProvider {

            // Verify that no renewal happened
            assertFalse(renewed, "renewCredentials should return false if no renewal mechanism succeeds");
            assertEquals(mockCredentials, wrapper.getCredentials(), "Credentials should remain unchanged if no renewal mechanism succeeds");
            // Note: Credentials interface does not have renew() method
        }
    }