diff --git a/src/structs.h b/src/structs.h
index 1508f47..8443a42 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -588,6 +588,9 @@
     XP_PREFIX_INV,	// "inv" prefix for bool option
 } xp_prefix_T;
 
+/*
+ * :set operator types
+ */
 typedef enum {
     OP_NONE = 0,
     OP_ADDING,		// "opt+=arg"