Update docs on public interface

lib/src/application_configuration.dart

@@ -20,9 +20,14 @@ import 'dart:io';
 import 'package:meta/meta.dart';
 import 'package:pub_semver/pub_semver.dart';
 
+/// Specify if and how to persists user objects.
 enum MetadataPersistenceMode {
-  plainText,
+  /// Persist [User] objects, but do not encrypt them.
+  unencrypted, 
+  /// Persist [User] objects in an encrypted store.
   encrypted,
+  /// Do not persist [User] objects.
+  disabled,
 }
 
 @immutable
@@ -31,10 +36,13 @@ class ApplicationConfiguration {
   final String appId;
 
   /// The [baseFilePath] is the [Directory] relative to which all local data for this application will be stored.
-  /// This data includes metadata for users and synchronized Realms.
+  /// 
+  /// This data includes metadata for users and synchronized Realms. If set, you must ensure that the [baseFilePath] 
+  /// directory exists.
   final Directory? baseFilePath;
 
   /// The [baseUrl] is the [Uri] used to reach the MongoDB Realm server.
+  /// 
   /// [baseUrl] only needs to be set if for some reason your application isn't hosted on realm.mongodb.com.
   /// This can be the case if you're testing locally or are using a pre-production environment.
   final Uri? baseUrl;
@@ -43,36 +51,45 @@ class ApplicationConfiguration {
   final Duration? defaultRequestTimeout;
 
   /// The [localAppName] is the friendly name identifying the current client application.
+  /// 
   /// This is typically used to differentiate between client applications that use the same
-  /// MongoDB Realm app. These can be the same conceptual app developed for different platforms, or
+  /// MongoDB Realm app. 
+  /// 
+  /// These can be the same conceptual app developed for different platforms, or
   /// significantly different client side applications that operate on the same data - e.g. an event managing
   /// service that has different clients apps for organizers and attendees.
   final String? localAppName;
 
-  /// The [localAppVersion]
+  /// The [localAppVersion] can be specified, if you wish to distinguish different client versions of the 
+  /// same application.
   final Version? localAppVersion;
 
   final MetadataPersistenceMode metadataPersistenceMode;
 
-  /// The encryption key for user metadata on this device.
-  /// This will not change the encryption key for individual Realms, which is set in the [Configuration]
+  /// The encryption key to use for user metadata on this device, if [metadataPersistenceMode] is 
+  /// [MetadataPersistenceMode.encrypted]. 
+  /// 
+  /// The [metadataEncryptionKey] must be exactly 64 bytes.
+  /// Setting this will not change the encryption key for individual Realms, which is set in the [Configuration].
   final List<int>? metadataEncryptionKey;
 
   /// The [HttpClient] that will be used for HTTP requests during authentication.
+  /// 
   /// You can use this to override the default http client handler and configure settings like proxies,
   /// client certificates, and cookies. While these are not required to connect to MongoDB Realm under
   /// normal circumstances, they can be useful if client devices are behind corporate firewall or use
   /// a more complex networking setup.
   final HttpClient httpClient;
 
+  /// Instantiates a new [ApplicationConfiguration].
   ApplicationConfiguration(
     this.appId, {
     this.baseUrl,
     this.baseFilePath,
     this.defaultRequestTimeout,
     this.localAppName,
     this.localAppVersion,
-    this.metadataPersistenceMode = MetadataPersistenceMode.plainText,
+    this.metadataPersistenceMode = MetadataPersistenceMode.unencrypted,
     this.metadataEncryptionKey,
     HttpClient? httpClient,
   }) : httpClient = httpClient ?? HttpClient();

lib/src/realm_class.dart

@@ -30,7 +30,7 @@ import 'realm_object.dart';
 import 'results.dart';
 
 // always expose with `show` to explicitly control the public API surface
-export "application_configuration.dart" show ApplicationConfiguration;
+export "application_configuration.dart" show ApplicationConfiguration, MetadataPersistenceMode;
 export 'package:realm_common/realm_common.dart'
     show Ignored, Indexed, MapTo, PrimaryKey, RealmError, RealmModel, RealmUnsupportedSetError, RealmStateError, RealmCollectionType, RealmPropertyType;
 export "configuration.dart" show Configuration, RealmSchema, SchemaObject;