diff --git a/fs_edit_preconditions.lua b/fs_edit_preconditions.lua
index a9ed50f..9e16c6c 100644
--- a/fs_edit_preconditions.lua
+++ b/fs_edit_preconditions.lua
@@ -1,31 +1,60 @@
 -- TODO: check inscription of a sign?
+-- TODO: check mesecons related things?
 
 -- Which diffrent types of preconditions are available?
 -- -> The following fields are part of a precondition:
 -- 	p_id		the ID/key of the precondition/prerequirement
--- 	p_type		selected from values_what; the staffs allow to use other
--- 			types like "function" or "has_item" - but that is not
--- 			supported here (cannot be edited or created; only be shown)
+-- 	p_type		selected from values_what
 -- 	p_value		used to store the subtype of p_type
 --
--- a state/variable:
+-- a state/variable ("state"):
 --	p_variable	name of a variable the player has read access to;
 --	                dropdown list with allowed options
 --	p_operator	selected from values_operator
 --	p_var_cmp_value can be set freely by the player
 --
--- a block in the world:
+-- a block in the world ("block"):
 --	p_pos		a position in the world; determined by asking the player
 --			to punch the block
 --	p_node		(follows from p_pos)
 --	p_param2	(follows from p_pos)
 --
--- a trade defined as an action: no variables needed (buy and pay stack follow
--- 			from the trade set as action)
+-- a trade defined as an action ("trade"): no variables needed (buy and pay stack
+-- 			follow from the trade set as action)
 --
--- an inventory:
+-- an inventory: ("player_inv", "npc_inv" or "block_inv")
 -- 	p_itemstack	an itemstack; needs to be a minetest.registered_item[..];
 -- 			size/count is also checked
+--
+-- the inventory of a block on the map: ("block_inv", in addition to the ones above)
+--	p_pos		a position in the world; determined by asking the player
+--			to punch the block
+--	p_inv_list_name name of the inventory list of the block
+--
+-- the player offered/gave the NPC an item: ("player_offered_item"):
+-- 	p_value    	an itemstack; needs to be a minetest.registered_item[..];
+-- 	                size/count is checked for some subtypes
+--      p_match_stack_size   does the NPC expect exactly one stack size - or is
+--                           more or less etc. also ok?
+--      p_item_group    are items of this group instead of the exact item name
+--                      also acceptable?
+--      p_item_desc     the description of the itemstack (set by another quest NPC
+--                      so that the player can distinguish it from other itemstacks
+--                      with the same item name; see action "npc_gives")
+--      p_item_quest_id Special ID to make sure that it is really the *right*
+--                      item and not just something the player faked with an
+--                      engraving table or something similar
+--
+-- a function ("function"): requires npc_master to create and edit
+--      p_value         the lua code to execute and evaulate
+--
+-- a custom function ("custon"):
+--      p_value         parameter for the custom function
+--
+-- depends on another option:
+--      p_value         name of the other option of this dialog that is considered
+--      p_fulfilled     shall option p_value be true or false?
+
 
 -- some helper lists for creating the formspecs and evaulating
 -- the player's answers:
@@ -46,9 +75,10 @@ local check_what = {
 }
 
 -- how to store these as p_type in the precondition:
-local values_what = {"", "state", "block", "trade", "player_inv", "npc_inv",
-	"block_inv", "player_offered_item",
-	-- requires npc_master priv
+local values_what = {"", "state", "block", "trade",
+	"player_inv", "npc_inv", "block_inv",
+	"player_offered_item",
+	-- "function" requires npc_master priv:
 	"function",
 	-- custom function (does not require npc_master priv)
 	"custom",