diff --git a/README.md b/README.md
index 5994461..2ae0e77 100644
--- a/README.md
+++ b/README.md
@@ -59,28 +59,45 @@ Secondly, there are the treasure spawning mods (TSMs). The task of a TSM is to s
 distribute the available treasures into the world. This is also called “treasure
 spawning”. How exactly the TSM spawns the treasures is completely up the TSM. But a
 TSM has to request Treasurer to get some random treasures to distribute. A TSM may
-optionally request to filter out treasures outside certain preciousness levels, so
-it can be 
+optionally request to filter out treasures outside certain preciousness levels
+and groups, so the result is a bit controllable and not completely random.
 Treasurer can not guarantee to return the requestet amount of treasures, it may
 return an empty table, for two reasons:
 
-* There is no TRM activated. There must be at least one to work
-* The preciousness filter filtered out. This problem can be fixed by installing more
-TRMs or by balancing the existing TRMs to cover as many preciousness levels as
-possible. It also may be that the range specified by the TSM was too small. It is
-recommended to keep the requested range at least of a size of 1.
-Treasurer does, however, guarantee that the returned treasures are always in the
-requested boundsa.
+* There is no TRM activated. There must be at least one to work.
+* The filters filtered out everything, leaving Treasurer with an empty treasure pool
+to choose from. This problem can be fixed by installing more TRMs or by balancing the
+existing TRMs to cover as many preciousness levels as possible. It also may be that
+the range specified by the TSM was too small. It is recommended to keep the
+requested range at least of a size of 1. Treasurer does, however, guarantee that
+the returned treasures are always in the requested bounds.
 
 A TSM has to at least depend on Treasurer.
-Like for TRMs, it is strongly recommended that a TSM does nothing more than spawning
-treasures. This does not exclude the possibility that a TSM does not depend
-on any other mod.
+Unlike for TRMs, it may not be a problem to also do some other stuff than just
+spawning treasures if it seems feasible. You may choose to make your TSM fully 
+dependant on Treasure, then it won’t work without Treasurer. You may also choose
+to only add an optional dependency on Treasurer. For this to work, your mod must
+now select its own treasures, which of course will only come from a rather limited
+pool.
+
+To check if the Treasurer mod is installed, you can use something like this in
+your code:
+
+```
+if(minetest.get_modpath("treasurer")~=nil) then
+	-- Treasurer is installed.
+	-- You can call Treasurer’s functions here.
+else
+	-- Treasurer is not installed.
+	-- You may write your replacement code here.
+	-- You can not call Treasurer’s funcitons here.
+end
+```
 
 There are two example TSMs. The first one is a very basic one and called “`tsm_gift_example`”.
 It gives a “welcome gift” (1 random treasure) to players who just joined the server
-or who respawn. The preciousness filter is not used. It does only depend on Treasurer.
-The second one is called “`tsm_chests_example`” and pretty advanced for an example.
+or who respawn. The preciousness and group filters are not used. It does only depend on
+Treasurer. The second one is called “`tsm_chests_example`” and pretty advanced for an example.
 It places chests of the mod “default” between 20 and 200 node lenghts below the water
 surface and puts 1-6 random treasures into these. The lower the chest, the higher
 the preciousness. It depends on treasurer and default (for the chests, of course).
@@ -108,7 +125,8 @@ certain treasure is then simply the rarity value divided by the sum.
 How “precious” an item is, is highly subjective and also not always easy to categorize.
 Preciousness in Treasurer’s terms should be therefore viewed as “utility” or as
 “reward level” or “strength” or even “beauty” or whatever positive attributes you can
-think of for items.
+think of for items. See the text file `GROUPS_AND_PRECIOUSNESS` for a rough
+guideline.
 So, if you create a TRM and your treasure is something you want the player work
 hard for, assign it a high preciousness. Everyday items that are already easy to
 obtain in normal gameplay certainly deserve a lower precious than items that are
diff --git a/init.lua b/init.lua
index f5b8dd1..fe117f1 100644
--- a/init.lua
+++ b/init.lua
@@ -210,7 +210,7 @@ end
     count: (optional) amount of items in the treasure. If this value is nil, treasurer assumes a default of 1.
     min_preciousness: (optional) don’t consider treasures with a lower preciousness. nil = no lower limit
     max_preciousness: (optional) don’t consider treasures with a higher preciousness. nil = no lower limit
-    treasurer_group: (optional): Only consider treasures which are members of at least one of the members of the provided Treasurer group table. nil = consider all groups
+    treasurer_groups: (optional): Only consider treasures which are members of at least one of the members of the provided Treasurer group table. nil = consider all groups
   returns: 
     a table of ItemStacks (the requested treasures) - may be empty
     on error, it returns false