diff --git a/core/modules/field/src/Plugin/migrate/source/d6/Field.php b/core/modules/field/src/Plugin/migrate/source/d6/Field.php
index 12dd0d92bfb9..d2c6392ae241 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/Field.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/Field.php
@@ -8,6 +8,10 @@ use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 /**
  * Drupal 6 field source from database.
  *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
+ *
  * @MigrateSource(
  *   id = "d6_field",
  *   source_module = "content"
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstance.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstance.php
index 263500729e18..ed302ea6dbba 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstance.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstance.php
@@ -10,6 +10,26 @@ use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 /**
  * Drupal 6 field instances source from database.
  *
+ * Available configuration keys:
+ * - node_type: (optional) The content type (machine name) to filter field
+ *   instances retrieved from the source. If omitted, all field instances are
+ *   retrieved.
+ *
+ * Example:
+ *
+ * @code
+ * source:
+ *   plugin: d6_field_instance
+ *   node_type: page
+ * @endcode
+ *
+ * In this example field instances of type page are retrieved from the source
+ * database.
+ *
+ * For additional configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
+ *
  * @MigrateSource(
  *   id = "d6_field_instance",
  *   source_module = "content"
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstanceOptionTranslation.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstanceOptionTranslation.php
index daaa1d290424..505aa1c9aafb 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstanceOptionTranslation.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstanceOptionTranslation.php
@@ -3,7 +3,11 @@
 namespace Drupal\field\Plugin\migrate\source\d6;
 
 /**
- * Gets field instance option label translations.
+ * Drupal 6 i18n field instance option labels source from database.
+ *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
  *
  * @MigrateSource(
  *   id = "d6_field_instance_option_translation",
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerFormDisplay.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerFormDisplay.php
index b64505a73d34..438b2198e613 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerFormDisplay.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerFormDisplay.php
@@ -5,7 +5,11 @@ namespace Drupal\field\Plugin\migrate\source\d6;
 use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 
 /**
- * The field instance per form display source class.
+ * Drupal 6 field instance per form display source from database.
+ *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
  *
  * @MigrateSource(
  *   id = "d6_field_instance_per_form_display",
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerViewMode.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerViewMode.php
index 59346bf0f41b..b571991084bc 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerViewMode.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldInstancePerViewMode.php
@@ -5,7 +5,11 @@ namespace Drupal\field\Plugin\migrate\source\d6;
 use Drupal\node\Plugin\migrate\source\d6\ViewModeBase;
 
 /**
- * The field instance per view mode source class.
+ * Drupal 6 field instance per view mode source from database.
+ *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
  *
  * @MigrateSource(
  *   id = "d6_field_instance_per_view_mode",
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldLabelDescriptionTranslation.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldLabelDescriptionTranslation.php
index cfc28b7ffd45..81edff92090e 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldLabelDescriptionTranslation.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldLabelDescriptionTranslation.php
@@ -5,7 +5,11 @@ namespace Drupal\field\Plugin\migrate\source\d6;
 use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 
 /**
- * Gets field label and description translations.
+ * Drupal 6 i18n field label and description source from database.
+ *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
  *
  * @MigrateSource(
  *   id = "d6_field_instance_label_description_translation",
diff --git a/core/modules/field/src/Plugin/migrate/source/d6/FieldOptionTranslation.php b/core/modules/field/src/Plugin/migrate/source/d6/FieldOptionTranslation.php
index 73bebb33c8d0..94aaeb43682c 100644
--- a/core/modules/field/src/Plugin/migrate/source/d6/FieldOptionTranslation.php
+++ b/core/modules/field/src/Plugin/migrate/source/d6/FieldOptionTranslation.php
@@ -3,7 +3,11 @@
 namespace Drupal\field\Plugin\migrate\source\d6;
 
 /**
- * Gets field option label translations.
+ * Drupal 6 i18n field option labels source from database.
+ *
+ * For available configuration keys, refer to the parent classes:
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
  *
  * @MigrateSource(
  *   id = "d6_field_option_translation",