diff --git a/docs/plugins/extending.md b/docs/plugins/extending.md
index 1807277c..a4a83673 100644
--- a/docs/plugins/extending.md
+++ b/docs/plugins/extending.md
@@ -57,6 +57,8 @@ A required dependency goes in `party.Plugin.Requires`, and activation fails when
 
 This replaces `PluginManager::exists` checks in WinterCMS.
 
+Optional here means optional at activation, not at compile time. A plugin that looks up a type declared in another plugin's package imports that package, so the other plugin still appears in its `go.mod`. Only `party.Plugin.Requires` leaves it out. `pact.OptionalMessage` is the way to integrate without that import.
+
 ## Model hooks and GORM callbacks
 
 A model reacts to its own lifecycle with GORM hook methods such as `BeforeSave`; [lagoon](../../modules/lagoon/README.md) names them as interfaces (`lagoon.HasBeforeSave`, `lagoon.HasBeforeDelete` and the rest) so you can assert them at compile time.