diff --git a/builtin/builtin.lua b/builtin/builtin.lua
index 7b39effb2..e529b7261 100644
--- a/builtin/builtin.lua
+++ b/builtin/builtin.lua
@@ -861,6 +861,14 @@ function minetest.get_connected_players()
 	return list
 end
 
+function minetest.hash_node_position(pos)
+	return (pos.z+32768)*65536*65536 + (pos.y+32768)*65536 + pos.x+32768
+end
+
+--
+-- Privileges
+--
+
 minetest.registered_privileges = {}
 function minetest.register_privilege(name, description)
 	minetest.registered_privileges[name] = description
diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index e253d2a28..ba610da8b 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -542,6 +542,8 @@ minetest.after(time, func, param)
 
 Random:
 minetest.get_connected_players() -> list of ObjectRefs
+minetest.hash_node_position({x=,y=,z=}) -> 48-bit integer
+^ Gives a unique hash number for a node position (16+16+16=48bit)
 
 Global objects:
 minetest.env - environment reference
@@ -768,6 +770,7 @@ Entity definition (register_entity)
 
 ABM (ActiveBlockModifier) definition (register_abm)
 {
+    -- In the following two fields, also group:groupname will work.
     nodenames = {"default:lava_source"},
     neighbors = {"default:water_source", "default:water_flowing"}, -- (any of these)
      ^ If left out or empty, any neighbor will do
diff --git a/src/environment.cpp b/src/environment.cpp
index 0c6d829f5..001b53a40 100644
--- a/src/environment.cpp
+++ b/src/environment.cpp
@@ -646,27 +646,30 @@ public:
 					= abm->getRequiredNeighbors();
 			for(std::set<std::string>::iterator
 					i = required_neighbors_s.begin();
-					i != required_neighbors_s.end(); i++){
-				content_t c = ndef->getId(*i);
-				if(c == CONTENT_IGNORE)
-					continue;
-				aabm.required_neighbors.insert(c);
+					i != required_neighbors_s.end(); i++)
+			{
+				ndef->getIds(*i, aabm.required_neighbors);
 			}
 			// Trigger contents
 			std::set<std::string> contents_s = abm->getTriggerContents();
 			for(std::set<std::string>::iterator
-					i = contents_s.begin(); i != contents_s.end(); i++){
-				content_t c = ndef->getId(*i);
-				if(c == CONTENT_IGNORE)
-					continue;
-				std::map<content_t, std::list<ActiveABM> >::iterator j;
-				j = m_aabms.find(c);
-				if(j == m_aabms.end()){
-					std::list<ActiveABM> aabmlist;
-					m_aabms[c] = aabmlist;
+					i = contents_s.begin(); i != contents_s.end(); i++)
+			{
+				std::set<content_t> ids;
+				ndef->getIds(*i, ids);
+				for(std::set<content_t>::const_iterator k = ids.begin();
+						k != ids.end(); k++)
+				{
+					content_t c = *k;
+					std::map<content_t, std::list<ActiveABM> >::iterator j;
 					j = m_aabms.find(c);
+					if(j == m_aabms.end()){
+						std::list<ActiveABM> aabmlist;
+						m_aabms[c] = aabmlist;
+						j = m_aabms.find(c);
+					}
+					j->second.push_back(aabm);
 				}
-				j->second.push_back(aabm);
 			}
 		}
 	}
diff --git a/src/nodedef.cpp b/src/nodedef.cpp
index 4b0c4b288..da74c8ce5 100644
--- a/src/nodedef.cpp
+++ b/src/nodedef.cpp
@@ -380,6 +380,25 @@ public:
 		getId(name, id);
 		return id;
 	}
+	virtual void getIds(const std::string &name, std::set<content_t> &result)
+			const
+	{
+		if(name.substr(0,6) != "group:"){
+			content_t id = CONTENT_IGNORE;
+			if(getId(name, id))
+				result.insert(id);
+			return;
+		}
+		std::string group = name.substr(6);
+		for(u16 id=0; id<=MAX_CONTENT; id++)
+		{
+			const ContentFeatures &f = m_content_features[id];
+			if(f.name == "") // Quickly discard undefined nodes
+				continue;
+			if(itemgroup_get(f.groups, group) != 0)
+				result.insert(id);
+		}
+	}
 	virtual const ContentFeatures& get(const std::string &name) const
 	{
 		content_t id = CONTENT_IGNORE;
diff --git a/src/nodedef.h b/src/nodedef.h
index a7ffa5a2e..753bea0ed 100644
--- a/src/nodedef.h
+++ b/src/nodedef.h
@@ -238,6 +238,9 @@ public:
 	virtual const ContentFeatures& get(const MapNode &n) const=0;
 	virtual bool getId(const std::string &name, content_t &result) const=0;
 	virtual content_t getId(const std::string &name) const=0;
+	// Allows "group:name" in addition to regular node names
+	virtual void getIds(const std::string &name, std::set<content_t> &result)
+			const=0;
 	virtual const ContentFeatures& get(const std::string &name) const=0;
 	
 	virtual void serialize(std::ostream &os)=0;
@@ -254,6 +257,9 @@ public:
 	virtual const ContentFeatures& get(const MapNode &n) const=0;
 	virtual bool getId(const std::string &name, content_t &result) const=0;
 	virtual content_t getId(const std::string &name) const=0;
+	// Allows "group:name" in addition to regular node names
+	virtual void getIds(const std::string &name, std::set<content_t> &result)
+			const=0;
 	// If not found, returns the features of CONTENT_IGNORE
 	virtual const ContentFeatures& get(const std::string &name) const=0;