Clean up wording of client usage expectations

pkg/analysis_server/lib/plugin/index/index_core.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analysis_server.plugin.index.index_core;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/services/index/index.dart';
@@ skipping 12 matching lines @@
 
 /**
  * An object that can have a [Relationship] with various [Location]s in a code
  * base. The object is abstractly represented by a [kind] and an [offset] within
  * a [source].
  *
  * Clients must ensure that two distinct objects in the same source cannot have
  * the same kind and offset. Failure to do so will make it impossible for
  * clients to identify the model element corresponding to the indexable object.
  *
- * Clients are expected to subtype this class when implementing plugins.
+ * Clients may implement this class when implementing plugins.
  */
 abstract class IndexableObject {
   /**
    * Return the absolute path of the file containing the indexable object.
    */
   String get filePath;
 
   /**
    * Return the kind of this object.
    */
   IndexableObjectKind get kind;
 
   /**
    * Return the offset of the indexable object within its source.
    */
   int get offset;
 }
 
 /**
  * The kind associated with an [IndexableObject].
  *
- * Clients are expected to implement this class when implementing plugins.
+ * Clients may implement this class when implementing plugins.
  */
 abstract class IndexableObjectKind {
   /**
    * The next available index for a newly created kind of indexable object.
    */
   static int _nextIndex = 0;
 
   /**
    * A table mapping indexes to object kinds.
    */
@@ skipping 58 matching lines @@
     if (_registry.containsKey(index)) {
       throw new ArgumentError('duplicate index for kind: $index');
     }
     _registry[index] = kind;
   }
 }
 
 /**
  * An object used to add relationships to the index.
  *
- * Clients are expected to subtype this class when implementing plugins.
+ * Clients may implement this class when implementing plugins.
  */
 abstract class IndexContributor {
   /**
    * Contribute relationships existing in the given [object] to the given
    * index [store] in the given [context].
    */
   void contributeTo(IndexStore store, AnalysisContext context, Object object);
 }
 
 /**
  * An object that stores information about the relationships between locations
  * in a code base.
  *
- * Clients are not expected to subtype this class.
+ * Clients may not extend, implement or mix-in this class.
  */
 abstract class IndexStore {
   /**
    * Remove all of the information from the index.
    */
   void clear();
 
   /**
    * Return a future that completes with the locations that have the given
    * [relationship] with the given [indexable] object.
@@ skipping 62 matching lines @@
 }
 
 /**
  * Instances of the class [Location] represent a location related to an
  * indexable object.
  *
  * The location is expressed as an offset and length, but the offset is relative
  * to the source containing the indexable object rather than the start of the
  * indexable object within that source.
  *
- * Clients are not expected to subtype this class.
+ * Clients may not extend, implement or mix-in this class.
  */
 abstract class Location {
   /**
    * An empty list of locations.
    */
   static const List<Location> EMPTY_LIST = const <Location>[];
 
   /**
    * Return the indexable object containing this location.
    */
@@ skipping 18 matching lines @@
    * Return the offset of this location within the source containing the
    * indexable object.
    */
   int get offset;
 }
 
 /**
  * A relationship between an indexable object and a location. Relationships are
  * identified by a globally unique identifier.
  *
- * Clients are not expected to subtype this class.
+ * Clients may not extend, implement or mix-in this class.
  */
 abstract class Relationship {
   /**
    * Return a relationship that has the given [identifier]. If the relationship
    * has already been created, then it will be returned, otherwise a new
    * relationship will be created
    */
   factory Relationship(String identifier) =>
       RelationshipImpl.getRelationship(identifier);
 }