diff --git a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
index 42a5fcc..b8d97b8 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -16,11 +16,13 @@
  * The base class for source plugins.
  *
  * Available configuration keys:
- * - cache_counts: (optional) (boolean) If set cache the source count.
- * - skip_count: (optional) (boolean) If set not attempt to count the source.
- * - track_changes: (optional) (boolean) If set track changes to incoming data.
- * - high_water_property: It is an array of single value (optional table alias)
- *   which have the high_water_property corresponding to it.
+ * - cache_counts: (optional) If set cache the source count.
+ * - skip_count: (optional) If set not attempt to count the source.
+ * - track_changes: (optional) If set track changes to incoming data.
+ * - high_water_property: (optional) It is an array of single value (optional
+ *   table alias) which have the high_water_property corresponding to it.
+ *
+ * The high_water_property and track_changes are mutually exclusive.
  *
  * Example:
  *
@@ -28,22 +30,28 @@
  * source:
  *   plugin: some_source_plugin_name
  *   cache_counts: true
- *   skip_count: true
  *   track_changes: true
  * @endcode
  *
- * The highwater mark or track changes not should be set at the same time.
- * They are both designed to solve the same problem.
+ * This example uses the plugin "some_source_plugin_name" and caches the count
+ * of available source records to save calculating every time count() is called.
+ * Changes to incoming data are watched (because track_changes is true) which
+ * can affect the result of prepareRow().
  *
  * Example:
  *
  * @code
  * source:
  *   plugin: some_source_plugin_name
+ *   skip_count: true
  *   high_water_property:
  *     name: something
  * @endcode
  *
+ * In this example skip_count is true which means count() will not attempt to
+ * count the available source records, but just always return -1 instead. The
+ * high_water_property defines which field marks the progress of the migration.
+ *
  * @see \Drupal\migrate\Plugin\MigratePluginManager
  * @see \Drupal\migrate\Annotation\MigrateSource
  * @see \Drupal\migrate\Plugin\MigrateSourceInterface