diff --git a/modules/src/data/pmap.h b/modules/src/data/pmap.h
index a7980a3a3..dd17f1c24 100644
--- a/modules/src/data/pmap.h
+++ b/modules/src/data/pmap.h
@@ -1,6 +1,9 @@
 #ifndef PMAP_H
 #define PMAP_H
 
+/* A bidirectional multimap, storing (left, right) tuples.
+ */
+
 struct pmap_node
 {
 	void* left;
@@ -23,10 +26,33 @@ struct pmap
 		int max; \
 	}
 
+/** Adds a new relation `(left -> right)` to the map
+ * if `left` is not present. Otherwise replaces the
+ * `right` associated with the first `left`.
+ *
+ * Use this in normal map mode.
+ */
 extern void pmap_put(void* map, void* left, void* right);
+
+/** Adds a new relation to the map if that relation does
+ * not already exist.
+ *
+ * Use this in multimap mode.
+ */
 extern void pmap_add(void* map, void* left, void* right);
+
+/** Removes a relation from the map.
+ *
+ * Use this in multimap mode.
+ */
 extern void pmap_remove(void* map, void* left, void* right);
+
+/** Given a `left`, find the first matching `right`.
+ */
 extern void* pmap_findleft(void* map, void* left);
+
+/** Given a `right`, find the first matching `left`.
+ */
 extern void* pmap_findright(void* map, void* right);
 
 #endif
diff --git a/modules/src/data/smap.c b/modules/src/data/smap.c
index 35e594997..abc8d180e 100644
--- a/modules/src/data/smap.c
+++ b/modules/src/data/smap.c
@@ -26,7 +26,7 @@ static void append(void* mapp, const char* key, void* value)
 }
 
 
-void smap_put(struct smap *mapp, const char* key, void* value)
+void smap_put(void *mapp, const char* key, void* value)
 {
     struct smap* map = mapp;
     int i;
@@ -44,34 +44,36 @@ void smap_put(struct smap *mapp, const char* key, void* value)
     append(map, key, value);
 }
 
-void smap_init(struct smap *mapp)
+void smap_init(void *mapp)
 {
-	mapp->count = 0;
-	mapp->item = NULL;
-	mapp->max = 0;
+    struct smap* map = mapp;
+	map->count = 0;
+	map->item = NULL;
+	map->max = 0;
 }
 
 
-void smap_free(struct smap *mapp, int free_key, int free_value)
+void smap_free(void *mapp, int free_key, int free_value)
 {
+    struct smap* map = mapp;
 	int i;
-    for (i=0; i<mapp->count; i++)
+    for (i=0; i<map->count; i++)
     {
-        struct smap_node* node = &mapp->item[i];
+        struct smap_node* node = &map->item[i];
         if (free_key)
         {
-        	free(node->left);
+        	free((void*) node->left);
         }
         if (free_value)
         {
         	free(node->right);
         }
     }
-	mapp->count = 0;
-	free(mapp->item);
+	map->count = 0;
+	free(map->item);
 }
 
-void smap_add(struct smap *mapp, const char* key, void* value)
+void smap_add(void *mapp, const char* key, void* value)
 {
     struct smap* map = mapp;
     int i;
@@ -86,7 +88,7 @@ void smap_add(struct smap *mapp, const char* key, void* value)
     append(map, key, value);
 }
 
-void* smap_get(struct smap *mapp, const char* left)
+void* smap_get(void *mapp, const char* left)
 {
     struct smap* map = mapp;
     int i;
diff --git a/modules/src/data/smap.h b/modules/src/data/smap.h
index 184c2b176..8e82639f7 100644
--- a/modules/src/data/smap.h
+++ b/modules/src/data/smap.h
@@ -6,9 +6,11 @@
 #ifndef SMAP_H
 #define SMAP_H
 
+/* A string multimap (each key can have multiple values). */
+
 struct smap_node
 {
-	char* left;
+	const char* left;
 	void* right;
 };
 
@@ -23,36 +25,45 @@ struct smap
 
 #define SMAPOF(RIGHT) \
 	struct { \
-		struct { char* left; RIGHT* right; }* item; \
+		struct { const char* left; RIGHT* right; }* item; \
 		int count; \
 		int max; \
 	}
 
-/** Initializes a string map and returns the initialized
- *  handle in `mapp`.
+/** Initializes a string map. Optional; a zero-initialised map
+ * structure is a valid empty map.
  */
-extern void smap_init(struct smap *mapp);
-/** Adds a new item with name `key` in the string map if
- *  it does not already exist, otherwise replaces the
- *  value `value` associated with the existing `key`.
- */
-extern void smap_put(struct smap *mapp, const char* key, void* value);
-/** Adds a new item in a string map only if `key` does
- *  not already exist in the string map.
- */
-extern void smap_add(struct smap *mapp, const char* key, void* value);
-/** Returns the value associated with the specified `key`, returns
- *  NULL if `key` is not present in the string map.
+extern void smap_init(void *mapp);
+
+/** Adds a new item with name `key` in the string map if it does not already
+ * exist. Otherwise replaces the value `value` associated with the existing
+ * `key`.
  *
+ * Use this for normal map mode.
  */
-extern void* smap_get(struct smap* mapp, const char* key);
+extern void smap_put(void *mapp, const char* key, void* value);
+
+/** Adds a new item with name `key` and value `value`. If that relation already
+ * exists, nothing happens.
+ *
+ * Use this for multimap mode.
+ */
+extern void smap_add(void *mapp, const char* key, void* value);
+
+/** Returns the first value associated with the specified `key`. Returns NULL
+ * if `key` is not present in the string map.
+ *
+ * Use this in normal map mode.
+ */
+extern void* smap_get(void* mapp, const char* key);
+
 /** Frees the data structure associated with the string map.
  *  Also frees the memory associated with the key if
  *  `free_key` is non-zero, and free the memory associated
  *  with the value if `free_value` is non-zero.
  *
  */
-extern void smap_free(struct smap *mapp, int free_key, int free_value);
+extern void smap_free(void *mapp, int free_key, int free_value);
 
 #endif
 
diff --git a/modules/src/data/stringlist.c b/modules/src/data/stringlist.c
index 39f125697..e947ea58f 100644
--- a/modules/src/data/stringlist.c
+++ b/modules/src/data/stringlist.c
@@ -39,7 +39,7 @@ void stringlist_free(struct stringlist* list, int freedata)
 		struct stringfragment* next = f->next;
 		if (freedata)
 		{
-			free(f->data);
+			free((void*) f->data);
 			f->data = NULL;
 		}
 		free(f);
@@ -54,7 +54,7 @@ void stringlist_init(struct stringlist* list)
 }
 
 
-char* stringlist_get(struct stringlist *list, int index)
+const char* stringlist_get(struct stringlist *list, int index)
 {
 	struct stringfragment* f = list->first;
 	int i = 0;
diff --git a/modules/src/data/stringlist.h b/modules/src/data/stringlist.h
index b3c6ae8e6..b104314d8 100644
--- a/modules/src/data/stringlist.h
+++ b/modules/src/data/stringlist.h
@@ -3,7 +3,7 @@
 
 struct stringfragment
 {
-	char* data;
+	const char* data;
 	struct stringfragment* next;
 };
 
@@ -18,7 +18,7 @@ extern void stringlist_addall(struct stringlist* list, struct stringlist* src);
 extern void stringlist_free(struct stringlist* list, int freedata);
 extern void stringlist_init(struct stringlist* list);
 extern int stringlist_count(struct stringlist *list);
-extern char* stringlist_get(struct stringlist *list, int index);
+extern const char* stringlist_get(struct stringlist *list, int index);
 
 
 #endif