diff -r 425d4279856f -r 35f06c5eeb0e src/cx/iterator.h
--- a/src/cx/iterator.h	Sun May 21 11:52:58 2023 +0200
+++ b/src/cx/iterator.h	Sun May 21 14:03:21 2023 +0200
@@ -51,6 +51,8 @@
 
     /**
      * Returns a pointer to the current element.
+     *
+     * When valid returns false, the behavior of this function is undefined.
      */
     __attribute__ ((__nonnull__))
     void *(*current)(void const *);
@@ -63,12 +65,16 @@
 
     /**
      * Advances the iterator.
+     *
+     * When valid returns false, the behavior of this function is undefined.
      */
     __attribute__ ((__nonnull__))
     void (*next)(void *);
 
     /**
      * Flag current element for removal, if possible.
+     *
+     * When valid returns false, the behavior of this function is undefined.
      */
     __attribute__ ((__nonnull__))
     bool (*flag_removal)(void *);