diff --git a/subiquity/models/source.py b/subiquity/models/source.py
index 4e576651b..b31e13b5b 100644
--- a/subiquity/models/source.py
+++ b/subiquity/models/source.py
@@ -67,7 +67,12 @@ def __attrs_post_init__(self):
 
 
 class BridgeKernelReason(enum.Enum):
+    # When bridge_reasons contains "drivers", some driver packages are known to
+    # be behind, so we should fall back to the bridge kernel.
     DRIVERS = "drivers"
+    # When bridge_reasons contains "zfs", we should use the bridge kernel as
+    # the default kernel is not yet known to the kernel team to be sufficiently
+    # stable.
     ZFS = "zfs"
 
 
diff --git a/subiquity/server/controllers/kernel.py b/subiquity/server/controllers/kernel.py
index 87dd87ac7..6076e5be8 100644
--- a/subiquity/server/controllers/kernel.py
+++ b/subiquity/server/controllers/kernel.py
@@ -113,6 +113,9 @@ def _confirmed(self):
 
     def _drivers_decided(self):
         drivers_controller = self.app.controllers.Drivers
+        # while the term DRIVERS is used here, only some drivers are expected
+        # to trigger bridge kernel fallback, and only then if DRIVERS is listed
+        # as one of the bridge_reasons.
         self._maybe_set_bridge_kernel(
             BridgeKernelReason.DRIVERS,
             drivers_controller.model.do_install