diff --git a/src/asdf-utils.lisp b/src/asdf-utils.lisp
index 15c8bd50..ba0ef8e0 100644
--- a/src/asdf-utils.lisp
+++ b/src/asdf-utils.lisp
@@ -55,6 +55,12 @@ DIRECTORY."
   "Return a list of all the required systems for SYSTEM topologically
 sorted by load order."
   (with-recursive-compile-bundle-op
+    ;; ASDF:REQUIRED-COMPONENTS traverses the dependency operations
+    ;; required to perform :GOAL-OPERATION on the provided system,
+    ;; returning a list of the components involved that have
+    ;; :COMPONENT-TYPE.
+    ;;
+    ;; TODO: what exactly do :OTHER-SYSTEMS and :KEEP-OPERATION do?
     (asdf:required-components system
                               :other-systems t
                               :component-type 'asdf:system