diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d35e774e9..87a0499b6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -276,6 +276,7 @@ set(SRB2_LUA_SOURCES
 	lua_hudlib.c
 	lua_infolib.c
 	lua_maplib.c
+	lua_taglib.c
 	lua_mathlib.c
 	lua_mobjlib.c
 	lua_playerlib.c
diff --git a/src/blua/Makefile.cfg b/src/blua/Makefile.cfg
index eae95ba3a..3a2962e65 100644
--- a/src/blua/Makefile.cfg
+++ b/src/blua/Makefile.cfg
@@ -47,6 +47,7 @@ OBJS:=$(OBJS) \
 	$(OBJDIR)/lua_skinlib.o \
 	$(OBJDIR)/lua_thinkerlib.o \
 	$(OBJDIR)/lua_maplib.o \
+	$(OBJDIR)/lua_taglib.o \
 	$(OBJDIR)/lua_polyobjlib.o \
 	$(OBJDIR)/lua_blockmaplib.o \
 	$(OBJDIR)/lua_hudlib.o
diff --git a/src/doomtype.h b/src/doomtype.h
index 4e13ba96d..08317c65a 100644
--- a/src/doomtype.h
+++ b/src/doomtype.h
@@ -379,4 +379,26 @@ Needed for some lua shenanigans.
 #define FIELDFROM( type, field, have, want ) \
 	(void *)((intptr_t)(field) - offsetof (type, have) + offsetof (type, want))
 
+typedef UINT8 bitarray_t;
+
+#define BIT_ARRAY_SIZE(n) (((n) + 7) >> 3)
+
+static inline int
+in_bit_array (const bitarray_t * const array, const int value)
+{
+	return (array[value >> 3] & (1<<(value & 7)));
+}
+
+static inline void
+set_bit_array (bitarray_t * const array, const int value)
+{
+	array[value >> 3] |= (1<<(value & 7));
+}
+
+static inline void
+unset_bit_array (bitarray_t * const array, const int value)
+{
+	array[value >> 3] &= ~(1<<(value & 7));
+}
+
 #endif //__DOOMTYPE__
diff --git a/src/lua_libs.h b/src/lua_libs.h
index 062a3fe50..aa0638683 100644
--- a/src/lua_libs.h
+++ b/src/lua_libs.h
@@ -93,6 +93,7 @@ int LUA_PlayerLib(lua_State *L);
 int LUA_SkinLib(lua_State *L);
 int LUA_ThinkerLib(lua_State *L);
 int LUA_MapLib(lua_State *L);
+int LUA_TagLib(lua_State *L);
 int LUA_PolyObjLib(lua_State *L);
 int LUA_BlockmapLib(lua_State *L);
 int LUA_HudLib(lua_State *L);
diff --git a/src/lua_maplib.c b/src/lua_maplib.c
index 95cc8c101..a3df28cca 100644
--- a/src/lua_maplib.c
+++ b/src/lua_maplib.c
@@ -1385,25 +1385,15 @@ static int lib_iterateSectors(lua_State *L)
 
 static int lib_getSector(lua_State *L)
 {
-	int field;
 	INLEVEL
-	lua_settop(L, 2);
-	lua_remove(L, 1); // dummy userdata table is unused.
-	if (lua_isnumber(L, 1))
+	if (lua_isnumber(L, 2))
 	{
-		size_t i = lua_tointeger(L, 1);
+		size_t i = lua_tointeger(L, 2);
 		if (i >= numsectors)
 			return 0;
 		LUA_PushUserdata(L, &sectors[i], META_SECTOR);
 		return 1;
 	}
-	field = luaL_checkoption(L, 1, NULL, array_opt);
-	switch(field)
-	{
-	case 0: // iterate
-		lua_pushcfunction(L, lib_iterateSectors);
-		return 1;
-	}
 	return 0;
 }
 
@@ -1489,25 +1479,15 @@ static int lib_iterateLines(lua_State *L)
 
 static int lib_getLine(lua_State *L)
 {
-	int field;
 	INLEVEL
-	lua_settop(L, 2);
-	lua_remove(L, 1); // dummy userdata table is unused.
-	if (lua_isnumber(L, 1))
+	if (lua_isnumber(L, 2))
 	{
-		size_t i = lua_tointeger(L, 1);
+		size_t i = lua_tointeger(L, 2);
 		if (i >= numlines)
 			return 0;
 		LUA_PushUserdata(L, &lines[i], META_LINE);
 		return 1;
 	}
-	field = luaL_checkoption(L, 1, NULL, array_opt);
-	switch(field)
-	{
-	case 0: // iterate
-		lua_pushcfunction(L, lib_iterateLines);
-		return 1;
-	}
 	return 0;
 }
 
@@ -2358,15 +2338,13 @@ int LUA_MapLib(lua_State *L)
 		//lua_setfield(L, -2, "__len");
 	lua_pop(L, 1);
 
-	lua_newuserdata(L, 0);
-		lua_createtable(L, 0, 2);
-			lua_pushcfunction(L, lib_getSector);
-			lua_setfield(L, -2, "__index");
-
-			lua_pushcfunction(L, lib_numsectors);
-			lua_setfield(L, -2, "__len");
-		lua_setmetatable(L, -2);
-	lua_setglobal(L, "sectors");
+	LUA_PushTaggableObjectArray(L, "sectors",
+			lib_iterateSectors,
+			lib_getSector,
+			lib_numsectors,
+			tags_sectors,
+			&numsectors, &sectors,
+			sizeof (sector_t), META_SECTOR);
 
 	lua_newuserdata(L, 0);
 		lua_createtable(L, 0, 2);
@@ -2378,15 +2356,13 @@ int LUA_MapLib(lua_State *L)
 		lua_setmetatable(L, -2);
 	lua_setglobal(L, "subsectors");
 
-	lua_newuserdata(L, 0);
-		lua_createtable(L, 0, 2);
-			lua_pushcfunction(L, lib_getLine);
-			lua_setfield(L, -2, "__index");
-
-			lua_pushcfunction(L, lib_numlines);
-			lua_setfield(L, -2, "__len");
-		lua_setmetatable(L, -2);
-	lua_setglobal(L, "lines");
+	LUA_PushTaggableObjectArray(L, "lines",
+			lib_iterateLines,
+			lib_getLine,
+			lib_numlines,
+			tags_lines,
+			&numlines, &lines,
+			sizeof (line_t), META_LINE);
 
 	lua_newuserdata(L, 0);
 		lua_createtable(L, 0, 2);
diff --git a/src/lua_mobjlib.c b/src/lua_mobjlib.c
index 7aae18c90..134f104ee 100644
--- a/src/lua_mobjlib.c
+++ b/src/lua_mobjlib.c
@@ -22,8 +22,6 @@
 #include "lua_hud.h" // hud_running errors
 #include "lua_hook.h" // hook_cmd_running errors
 
-static const char *const array_opt[] ={"iterate",NULL};
-
 enum mobj_e {
 	mobj_valid = 0,
 	mobj_x,
@@ -1003,25 +1001,15 @@ static int lib_iterateMapthings(lua_State *L)
 
 static int lib_getMapthing(lua_State *L)
 {
-	int field;
 	INLEVEL
-	lua_settop(L, 2);
-	lua_remove(L, 1); // dummy userdata table is unused.
-	if (lua_isnumber(L, 1))
+	if (lua_isnumber(L, 2))
 	{
-		size_t i = lua_tointeger(L, 1);
+		size_t i = lua_tointeger(L, 2);
 		if (i >= nummapthings)
 			return 0;
 		LUA_PushUserdata(L, &mapthings[i], META_MAPTHING);
 		return 1;
 	}
-	field = luaL_checkoption(L, 1, NULL, array_opt);
-	switch(field)
-	{
-	case 0: // iterate
-		lua_pushcfunction(L, lib_iterateMapthings);
-		return 1;
-	}
 	return 0;
 }
 
@@ -1068,14 +1056,13 @@ int LUA_MobjLib(lua_State *L)
 		lua_setfield(L, -2, "__len");
 	lua_pop(L,1);
 
-	lua_newuserdata(L, 0);
-		lua_createtable(L, 0, 2);
-			lua_pushcfunction(L, lib_getMapthing);
-			lua_setfield(L, -2, "__index");
+	LUA_PushTaggableObjectArray(L, "mapthings",
+			lib_iterateMapthings,
+			lib_getMapthing,
+			lib_nummapthings,
+			tags_mapthings,
+			&nummapthings, &mapthings,
+			sizeof (mapthing_t), META_MAPTHING);
 
-			lua_pushcfunction(L, lib_nummapthings);
-			lua_setfield(L, -2, "__len");
-		lua_setmetatable(L, -2);
-	lua_setglobal(L, "mapthings");
 	return 0;
 }
diff --git a/src/lua_script.c b/src/lua_script.c
index eb4737f76..ee60a41c6 100644
--- a/src/lua_script.c
+++ b/src/lua_script.c
@@ -53,6 +53,7 @@ static lua_CFunction liblist[] = {
 	LUA_SkinLib, // skin_t, skins[]
 	LUA_ThinkerLib, // thinker_t
 	LUA_MapLib, // line_t, side_t, sector_t, subsector_t
+	LUA_TagLib, // tags
 	LUA_PolyObjLib, // polyobj_t
 	LUA_BlockmapLib, // blockmap stuff
 	LUA_HudLib, // HUD stuff
@@ -739,25 +740,37 @@ void LUA_PushLightUserdata (lua_State *L, void *data, const char *meta)
 // Pushes it to the stack and stores it in the registry.
 void LUA_PushUserdata(lua_State *L, void *data, const char *meta)
 {
+	if (LUA_RawPushUserdata(L, data) == LPUSHED_NEW)
+	{
+		luaL_getmetatable(L, meta);
+		lua_setmetatable(L, -2);
+	}
+}
+
+// Same as LUA_PushUserdata but don't set a metatable yet.
+lpushed_t LUA_RawPushUserdata(lua_State *L, void *data)
+{
+	lpushed_t status = LPUSHED_NIL;
+
 	void **userdata;
 
 	if (!data) { // push a NULL
 		lua_pushnil(L);
-		return;
+		return status;
 	}
 
 	lua_getfield(L, LUA_REGISTRYINDEX, LREG_VALID);
 	I_Assert(lua_istable(L, -1));
+
 	lua_pushlightuserdata(L, data);
 	lua_rawget(L, -2);
+
 	if (lua_isnil(L, -1)) { // no userdata? deary me, we'll have to make one.
 		lua_pop(L, 1); // pop the nil
 
 		// create the userdata
 		userdata = lua_newuserdata(L, sizeof(void *));
 		*userdata = data;
-		luaL_getmetatable(L, meta);
-		lua_setmetatable(L, -2);
 
 		// Set it in the registry so we can find it again
 		lua_pushlightuserdata(L, data); // k (store the userdata via the data's pointer)
@@ -765,8 +778,15 @@ void LUA_PushUserdata(lua_State *L, void *data, const char *meta)
 		lua_rawset(L, -4);
 
 		// stack is left with the userdata on top, as if getting it had originally succeeded.
+
+		status = LPUSHED_NEW;
 	}
+	else
+		status = LPUSHED_EXISTING;
+
 	lua_remove(L, -2); // remove LREG_VALID
+
+	return status;
 }
 
 // When userdata is freed, use this function to remove it from Lua.
@@ -1681,3 +1701,36 @@ int Lua_optoption(lua_State *L, int narg,
 			return i;
 	return -1;
 }
+
+void LUA_PushTaggableObjectArray
+(		lua_State *L,
+		const char *field,
+		lua_CFunction iterator,
+		lua_CFunction indexer,
+		lua_CFunction counter,
+		taggroup_t *garray[],
+		size_t * max_elements,
+		void * element_array,
+		size_t sizeof_element,
+		const char *meta)
+{
+	lua_newuserdata(L, 0);
+		lua_createtable(L, 0, 2);
+			lua_createtable(L, 0, 2);
+				lua_pushcfunction(L, iterator);
+				lua_setfield(L, -2, "iterate");
+
+				LUA_InsertTaggroupIterator(L, garray,
+						max_elements, element_array, sizeof_element, meta);
+
+				lua_createtable(L, 0, 1);
+					lua_pushcfunction(L, indexer);
+					lua_setfield(L, -2, "__index");
+				lua_setmetatable(L, -2);
+			lua_setfield(L, -2, "__index");
+
+			lua_pushcfunction(L, counter);
+			lua_setfield(L, -2, "__len");
+		lua_setmetatable(L, -2);
+	lua_setglobal(L, field);
+}
diff --git a/src/lua_script.h b/src/lua_script.h
index 79ba0bb38..2dc34446a 100644
--- a/src/lua_script.h
+++ b/src/lua_script.h
@@ -10,10 +10,14 @@
 /// \file  lua_script.h
 /// \brief Lua scripting basics
 
+#ifndef LUA_SCRIPT_H
+#define LUA_SCRIPT_H
+
 #include "m_fixed.h"
 #include "doomtype.h"
 #include "d_player.h"
 #include "g_state.h"
+#include "taglist.h"
 
 #include "blua/lua.h"
 #include "blua/lualib.h"
@@ -46,12 +50,6 @@ void LUA_LoadLump(UINT16 wad, UINT16 lump, boolean noresults);
 void LUA_DumpFile(const char *filename);
 #endif
 fixed_t LUA_EvalMath(const char *word);
-void LUA_PushLightUserdata(lua_State *L, void *data, const char *meta);
-void LUA_PushUserdata(lua_State *L, void *data, const char *meta);
-void LUA_InvalidateUserdata(void *data);
-void LUA_InvalidateLevel(void);
-void LUA_InvalidateMapthings(void);
-void LUA_InvalidatePlayer(player_t *player);
 void LUA_Step(void);
 void LUA_Archive(void);
 void LUA_UnArchive(void);
@@ -63,6 +61,42 @@ int Lua_optoption(lua_State *L, int narg,
 	const char *def, const char *const lst[]);
 void LUAh_NetArchiveHook(lua_CFunction archFunc);
 
+void LUA_PushTaggableObjectArray
+(		lua_State *L,
+		const char *field,
+		lua_CFunction iterator,
+		lua_CFunction indexer,
+		lua_CFunction counter,
+		taggroup_t *garray[],
+		size_t * max_elements,
+		void * element_array,
+		size_t sizeof_element,
+		const char *meta);
+
+void LUA_InsertTaggroupIterator
+(		lua_State *L,
+		taggroup_t *garray[],
+		size_t * max_elements,
+		void * element_array,
+		size_t sizeof_element,
+		const char * meta);
+
+typedef enum {
+	LPUSHED_NIL,
+	LPUSHED_NEW,
+	LPUSHED_EXISTING,
+} lpushed_t;
+
+void LUA_PushLightUserdata(lua_State *L, void *data, const char *meta);
+void LUA_PushUserdata(lua_State *L, void *data, const char *meta);
+lpushed_t LUA_RawPushUserdata(lua_State *L, void *data);
+
+void LUA_InvalidateUserdata(void *data);
+
+void LUA_InvalidateLevel(void);
+void LUA_InvalidateMapthings(void);
+void LUA_InvalidatePlayer(player_t *player);
+
 // Console wrapper
 void COM_Lua_f(void);
 
@@ -98,3 +132,5 @@ void COM_Lua_f(void);
 
 #define INLEVEL if (! ISINLEVEL)\
 return luaL_error(L, "This can only be used in a level!");
+
+#endif/*LUA_SCRIPT_H*/
diff --git a/src/taglist.c b/src/taglist.c
index b11216b6c..658605734 100644
--- a/src/taglist.c
+++ b/src/taglist.c
@@ -15,6 +15,11 @@
 #include "z_zone.h"
 #include "r_data.h"
 
+// Bit array of whether a tag exists for sectors/lines/things.
+bitarray_t tags_available[BIT_ARRAY_SIZE (MAXTAGS)];
+
+size_t num_tags;
+
 // Taggroups are used to list elements of the same tag, for iteration.
 // Since elements can now have multiple tags, it means an element may appear
 // in several taggroups at the same time. These are built on level load.
@@ -105,6 +110,33 @@ size_t Taggroup_Find (const taggroup_t *group, const size_t id)
 	return -1;
 }
 
+/// Iterate thru elements in a global taggroup.
+INT32 Taggroup_Iterate
+(		taggroup_t *garray[],
+		const size_t max_elements,
+		const mtag_t tag,
+		const size_t p)
+{
+	const taggroup_t *group;
+
+	if (tag == MTAG_GLOBAL)
+	{
+		if (p < max_elements)
+			return p;
+		return -1;
+	}
+
+	group = garray[(UINT16)tag];
+
+	if (group)
+	{
+		if (p < group->count)
+			return group->elements[p];
+		return -1;
+	}
+	return -1;
+}
+
 /// Add an element to a global taggroup.
 void Taggroup_Add (taggroup_t *garray[], const mtag_t tag, size_t id)
 {
@@ -120,6 +152,11 @@ void Taggroup_Add (taggroup_t *garray[], const mtag_t tag, size_t id)
 	if (Taggroup_Find(group, id) != (size_t)-1)
 		return;
 
+	if (! in_bit_array(tags_available, tag))
+		num_tags++;
+
+	set_bit_array(tags_available, tag);
+
 	// Create group if empty.
 	if (!group)
 	{
@@ -161,6 +198,11 @@ void Taggroup_Remove (taggroup_t *garray[], const mtag_t tag, size_t id)
 	if ((rempos = Taggroup_Find(group, id)) == (size_t)-1)
 		return;
 
+	if (in_bit_array(tags_available, tag))
+		num_tags--;
+
+	unset_bit_array(tags_available, tag);
+
 	// Strip away taggroup if no elements left.
 	if (!(newcount = --group->count))
 	{
@@ -209,6 +251,9 @@ void Taglist_InitGlobalTables(void)
 {
 	size_t i, j;
 
+	memset(tags_available, 0, sizeof tags_available);
+	num_tags = 0;
+
 	for (i = 0; i < MAXTAGS; i++)
 	{
 		tags_sectors[i] = NULL;
@@ -236,56 +281,17 @@ void Taglist_InitGlobalTables(void)
 
 INT32 Tag_Iterate_Sectors (const mtag_t tag, const size_t p)
 {
-	if (tag == MTAG_GLOBAL)
-	{
-		if (p < numsectors)
-			return p;
-		return -1;
-	}
-
-	if (tags_sectors[(UINT16)tag])
-	{
-		if (p < tags_sectors[(UINT16)tag]->count)
-			return tags_sectors[(UINT16)tag]->elements[p];
-		return -1;
-	}
-	return -1;
+	return Taggroup_Iterate(tags_sectors, numsectors, tag, p);
 }
 
 INT32 Tag_Iterate_Lines (const mtag_t tag, const size_t p)
 {
-	if (tag == MTAG_GLOBAL)
-	{
-		if (p < numlines)
-			return p;
-		return -1;
-	}
-
-	if (tags_lines[(UINT16)tag])
-	{
-		if (p < tags_lines[(UINT16)tag]->count)
-			return tags_lines[(UINT16)tag]->elements[p];
-		return -1;
-	}
-	return -1;
+	return Taggroup_Iterate(tags_lines, numlines, tag, p);
 }
 
 INT32 Tag_Iterate_Things (const mtag_t tag, const size_t p)
 {
-	if (tag == MTAG_GLOBAL)
-	{
-		if (p < nummapthings)
-			return p;
-		return -1;
-	}
-
-	if (tags_mapthings[(UINT16)tag])
-	{
-		if (p < tags_mapthings[(UINT16)tag]->count)
-			return tags_mapthings[(UINT16)tag]->elements[p];
-		return -1;
-	}
-	return -1;
+	return Taggroup_Iterate(tags_mapthings, nummapthings, tag, p);
 }
 
 INT32 Tag_FindLineSpecial(const INT16 special, const mtag_t tag)
diff --git a/src/taglist.h b/src/taglist.h
index 0e6d9f842..e5db08806 100644
--- a/src/taglist.h
+++ b/src/taglist.h
@@ -43,6 +43,10 @@ typedef struct
 	size_t count;
 } taggroup_t;
 
+extern bitarray_t tags_available[];
+
+extern size_t num_tags;
+
 extern taggroup_t* tags_sectors[];
 extern taggroup_t* tags_lines[];
 extern taggroup_t* tags_mapthings[];
@@ -51,6 +55,12 @@ void Taggroup_Add (taggroup_t *garray[], const mtag_t tag, size_t id);
 void Taggroup_Remove (taggroup_t *garray[], const mtag_t tag, size_t id);
 size_t Taggroup_Find (const taggroup_t *group, const size_t id);
 
+INT32 Taggroup_Iterate
+(		taggroup_t *garray[],
+		const size_t max_elements,
+		const mtag_t tag,
+		const size_t p);
+
 void Taglist_InitGlobalTables(void);
 
 INT32 Tag_Iterate_Sectors (const mtag_t tag, const size_t p);