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diff --git a/src/core-units/container.lisp b/src/core-units/container.lisp
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+;;;; units/container.lisp
+
+(in-package #:wheelwork)
+
+
+(defclass/std container ()
+  ((units :with :a))
+  (:documentation "Just a list of units. Made into a class so that
+  transformation affine transformations methods can be specialzied on
+  whole groups of units"))
+
+(defmethod drop-unit ((unit unit))
+  "Removes a unit from its container. Returns T if the unit actually was removed."
+  (when-let (container (unit-container unit))
+    (setf
+     (container-units container) (delete unit (container-units container))
+     (unit-container unit) nil)
+    t))
+
+(defmethod add-unit ((container container) (unit unit))
+  "Adds a unit to the end of a container (thus affecting render
+order). Makes sure to remove the unit from its current container if
+necessary."
+  (when (unit-container unit)
+    (drop-unit unit))
+  (push unit  (container-units container))
+  (setf (unit-container unit) container)
+  unit)
+
+(defmethod cleanup ((container container))
+  (dolist (u (container-units container))
+    (cleanup u)))