yl_speak_up.input_fs_manage_variables = function(player, formname, fields)
	local pname = player:get_player_name()
	if(fields and fields.back_from_msg) then
		yl_speak_up.show_fs(player, "manage_variables")
		return
	end
	-- leave this formspec
	if(fields and (fields.quit or fields.exit or fields.back)) then
		local last_fs = yl_speak_up.speak_to[pname][ "working_at" ]
		yl_speak_up.show_fs(player, last_fs)
		return
	-- add a new variable?
	elseif(fields and fields.add_variable) then
		local error_msg = ""
		if(not(fields.add_variable_name) or fields.add_variable_name == ""
		  or fields.add_variable_name:trim() == "") then
			error_msg = "Please enter the name of your variable!"
		-- limit names to something more sensible
		elseif(string.len(fields.add_variable_name) > 30) then
			error_msg = "The name of your variable name is too long.\n"..
					"Only up to 30 characters are allowed."
		elseif(string.len(fields.add_variable_name:trim()) < 2) then
			error_msg = "The name of your variable name is too short.\n"..
					"It has to be at least 2 characters long."
		else
			fields.add_variable_name = fields.add_variable_name:trim()
			local res = yl_speak_up.add_quest_variable(pname, fields.add_variable_name)
			-- not really an error msg here - but fascilitates output
			error_msg = "A new variable named\n     \""..
				minetest.formspec_escape(fields.add_variable_name)..
				"\"\nhas been created."
			if(not(res)) then
				error_msg = "Failed to create variable named\n      \""..
					minetest.formspec_escape(fields.add_variable_name).."\"."
			else
				-- slect this new variable
				local var_list = yl_speak_up.get_quest_variables(pname, true)
				-- make names of own variables shorter
				yl_speak_up.strip_pname_from_varlist(var_list, pname)
				table.sort(var_list)
				local index = table.indexof(var_list, fields.add_variable_name)
				if(index and index > -1) then
					yl_speak_up.speak_to[pname].tmp_index_variable = index + 1
				end
			end
		end
		yl_speak_up.show_fs(player, "msg", {
			input_to = "yl_speak_up:manage_variables",
			formspec = "size[6,2]"..
				"label[0.2,0.0;"..error_msg.."]"..
				"button[1.5,1.5;2,0.9;back_from_msg;Back]"})
		return
	-- show where this variable is used
	elseif(fields and fields.show_var_usage and fields.show_var_usage ~= "") then
		yl_speak_up.show_fs(player, "msg", {
			input_to = "yl_speak_up:manage_variables",
			formspec = yl_speak_up.fs_get_list_of_usage_of_variable(
					fields.list_var_names, pname, true,
					"back_from_msg",
					"Back to manage variables",
					-- not an internal variable
					false)
		})
		return
	end

	-- which variable is currently selected?
	local var_list = yl_speak_up.get_quest_variables(pname, true)
	-- make names of own variables shorter
	yl_speak_up.strip_pname_from_varlist(var_list, pname)
	table.sort(var_list)
	-- a var name was selected in the dropdown list
	if(fields and fields.list_var_names and fields.list_var_names ~= "") then
		local index = table.indexof(var_list, fields.list_var_names)
		if(fields.list_var_names == "Add variable:") then
			index = 0
		end
		if(index and index > -1) then
			yl_speak_up.speak_to[pname].tmp_index_variable = index + 1
		end
	end
	local var_name = var_list[ yl_speak_up.speak_to[pname].tmp_index_variable - 1]
	if(not(var_name)) then
		var_name = ""
	end


	-- delete (empty) variable
	if(fields
	  and ((fields.delete_variable and fields.delete_variable ~= "")
	    or (fields.delete_unused_variable and fields.delete_unused_variable ~= ""))
	  and var_name) then
		local text = yl_speak_up.del_quest_variable(pname, var_name, nil)
		yl_speak_up.show_fs(player, "msg", {
			input_to = "yl_speak_up:manage_variables",
                        formspec = "size[10,2]"..
                                "label[0.2,0.0;Trying to delete variable \""..
                                        minetest.formspec_escape(tostring(var_name))..
                                        "\":\n"..text.."]"..
                                "button[1.5,1.5;2,0.9;back_from_msg;Back]"})

		return

	-- revoke read or write access to a variable
	elseif(fields
	  and ((fields.revoke_player_var_read_access  and fields.revoke_player_var_read_access ~= "")
	    or (fields.revoke_player_var_write_access and fields.revoke_player_var_write_access ~= ""))
	  and var_name) then
		local right = "read"
		if(fields.revoke_player_var_write_access and fields.revoke_player_var_write_access ~= "") then
			right = "write"
		end
		-- which player are we talking about?
		local selected = yl_speak_up.speak_to[pname]["tmp_index_var_"..right.."_access"]
		local pl_with_access = yl_speak_up.get_access_list_for_var(var_name, pname, right.."_access")
		local tmp_list = {}
		for k, v in pairs(pl_with_access) do
			table.insert(tmp_list, k)
		end
		table.sort(tmp_list)
		local grant_to = ""
		if(selected > 1) then
			grant_to = tmp_list[ selected-1 ]
		end
		local error_msg = ""
		local pl_with_access = yl_speak_up.get_access_list_for_var(var_name, pname, right.."_access")
		if(not(grant_to) or grant_to == "") then
			error_msg = "For which player do you want to revoke "..right.." access?"
		elseif(pname ~= yl_speak_up.npc_owner[ n_id ]
		  and not(minetest.check_player_privs(pname, {npc_talk_master=true}))) then
			error_msg = "Only the owner of the NPC or players with\n"..
				    "the npc_talk_master priv can change this."
		elseif(not(pl_with_access[ grant_to ])) then
			error_msg = minetest.formspec_escape(grant_to).." doesn't have "..right..
				    " access\nto this variable. Nothing changed."
		-- try to revoke access
		elseif(not(yl_speak_up.manage_access_to_quest_variable(var_name, pname, grant_to,
									right.."_access", nil))) then
			error_msg = "An internal error occoured."
		else
			-- not really an error message here...rather a success message
			error_msg = "Revoked "..right.." access to variable\n\""..
				minetest.formspec_escape(var_name)..
				"\"\nfor player "..minetest.formspec_escape(grant_to)..".\n"..
				"Note: This will *not* affect existing preconditions/effects!"
		end
		yl_speak_up.show_fs(player, "msg", {
			input_to = "yl_speak_up:manage_variables",
			formspec = "size[6,2]"..
				"label[0.2,0.0;"..error_msg.."]"..
				"button[1.5,1.5;2,0.9;back_from_msg;Back]"})
		return

	-- grant read or write access to a variable
	elseif(fields
	  and ((fields.grant_player_var_read_access  and fields.grant_player_var_read_access ~= "")
	    or (fields.grant_player_var_write_access and fields.grant_player_var_write_access ~= ""))
	  and var_name) then
		local right = "read"
		if(fields.grant_player_var_write_access and fields.grant_player_var_write_access ~= "") then
			right = "write"
		end
		local grant_to = fields[ "grant_player_var_"..right.."_access"]
		local error_msg = ""
		local pl_with_access = yl_speak_up.get_access_list_for_var(var_name, pname, right.."_access")
		if(pname ~= yl_speak_up.npc_owner[ n_id ]
		  and not(minetest.check_player_privs(pname, {npc_talk_master=true}))) then
			error_msg = "Only the owner of the NPC or players with\n"..
				    "the npc_talk_master priv can change this."
		elseif(grant_to == pname) then
                        error_msg = "You already have "..right.." access to this variable."
		elseif(pl_with_access[ grant_to ]) then
			error_msg = minetest.formspec_escape(grant_to).." already has "..right..
				    " access\nto this variable."
		elseif(not(minetest.check_player_privs(grant_to, {interact=true}))) then
			error_msg = "Player \""..minetest.formspec_escape(grant_to).."\" not found."
		-- try to grant access
		elseif(not(yl_speak_up.manage_access_to_quest_variable(var_name, pname, grant_to,
									right.."_access", true))) then
			error_msg = "An internal error occoured."
		else
			-- not really an error message here...rather a success message
			error_msg = "Granted "..right.." access to variable\n\""..
				minetest.formspec_escape(var_name)..
				"\"\nto player "..minetest.formspec_escape(grant_to).."."
		end
		yl_speak_up.show_fs(player, "msg", {
			input_to = "yl_speak_up:manage_variables",
			formspec = "size[6,2]"..
				"label[0.2,0.0;"..error_msg.."]"..
				"button[1.5,1.5;2,0.9;back_from_msg;Back]"})
		return

	-- the player clicked on a name in the list of players with read or write access
	elseif(fields
	  and ((fields.list_var_read_access  and fields.list_var_read_access ~= "")
	    or (fields.list_var_write_access and fields.list_var_write_access ~= ""))
	  and var_name) then
		local right = "read"
		if(fields.list_var_write_access and fields.list_var_write_access ~= "") then
			right = "write"
		end
		local selected = fields[ "list_var_"..right.."_access"]
		local pl_with_access = yl_speak_up.get_access_list_for_var(var_name, pname, right.."_access")
		local tmp_list = {}
		for k, v in pairs(pl_with_access) do
			table.insert(tmp_list, k)
		end
		table.sort(tmp_list)
		local index = table.indexof(tmp_list, selected)
		if(selected == "Add player:") then
			index = 0
		end
		if(index and index > -1) then
			yl_speak_up.speak_to[pname]["tmp_index_var_"..right.."_access"] = index + 1
		end
		yl_speak_up.show_fs(player, "manage_variables")
		return

	-- a var name was selected in the dropdown list
	elseif(fields and fields.list_var_names and fields.list_var_names ~= "") then
		-- show the same formspec again, with a diffrent variable selected
		yl_speak_up.show_fs(player, "manage_variables")
		return
	end
	-- try to go back to the last formspec shown before this one
	if(not(yl_speak_up.speak_to[pname])) then
		return
	end
	local last_fs = yl_speak_up.speak_to[pname][ "working_at" ]
	yl_speak_up.show_fs(player, last_fs)
end


yl_speak_up.get_fs_manage_variables = function(player, param)
	local pname = player:get_player_name()
	-- variables owned by the player - including those with write access
	local var_list = yl_speak_up.get_quest_variables(pname, true)
	-- make names of own variables shorter
	yl_speak_up.strip_pname_from_varlist(var_list, pname)
	-- the yl_speak_up.create_dropdown_playerlist function needs a table - not a list
	local table_of_vars = {}
	for i, k in ipairs(var_list) do
		table_of_vars[ k ] = true
	end
	-- "Add variable:" is currently selected
	local additional_buttons = ""
	if(not(yl_speak_up.speak_to[pname].tmp_index_variable)
	   or yl_speak_up.speak_to[pname].tmp_index_variable == 1
	   or not(var_list[ yl_speak_up.speak_to[pname].tmp_index_variable - 1])) then
		yl_speak_up.speak_to[pname].tmp_index_variable = 1
		additional_buttons = "button[11.4,1.9;2.5,0.9;add_variable;Create variable]"..
			"tooltip[add_variable;Create a new varialbe with the name\n"..
				"you entered in the field to the left.]"

	else
		-- index 1 is "Add variable:"
		local k = var_list[ yl_speak_up.speak_to[pname].tmp_index_variable - 1]
		local pl_with_read_access = yl_speak_up.get_access_list_for_var(k, pname, "read_access")
		local pl_with_write_access = yl_speak_up.get_access_list_for_var(k, pname, "write_access")
		local add_read_button = ""
		local add_write_button = ""
		if(not(yl_speak_up.speak_to[pname].tmp_index_var_read_access)
		   or yl_speak_up.speak_to[pname].tmp_index_var_read_access == 1) then
			yl_speak_up.speak_to[pname].tmp_index_var_read_access = 1
			add_read_button = "button[12.9,2.9;1.0,0.9;add_read_access;Add]"..
				"tooltip[add_read_access;Grant the player whose name you entered\n"..
					"you entered in the field to the left read access\n"..
					"to your variable.]"
		end
		if(not(yl_speak_up.speak_to[pname].tmp_index_var_write_access)
		   or yl_speak_up.speak_to[pname].tmp_index_var_write_access == 1) then
			yl_speak_up.speak_to[pname].tmp_index_var_write_access = 1
			add_write_button = "button[12.9,3.9;1.0,0.9;add_write_access;Add]"..
				"tooltip[add_write_access;Grant the player whose name you entered\n"..
					"you entered in the field to the left *write* access\n"..
					"to your variable.]"
		end
		local list_of_npc_users = "- none -"
		local list_of_node_pos_users = "- none -"
		-- expand name of variable k again
		local k_long = yl_speak_up.add_pname_to_var(k, pname)
		-- which npc and which node_pos use this variable? create a list for display
		local c1 = 0
		local c2 = 0
		if(k_long
		  and yl_speak_up.player_vars[ k_long ]
		  and yl_speak_up.player_vars[ k_long ][ "$META$"]) then
			local npc_users = yl_speak_up.get_variable_metadata(k_long, "used_by_npc")
			c1 = #npc_users
			if(npc_users and c1 > 0) then
				list_of_npc_users = minetest.formspec_escape(table.concat(npc_users, ", "))
			end
			local node_pos_users = yl_speak_up.get_variable_metadata(k_long, "used_by_node_pos")
			c2 = #node_pos_users
			if(node_pos_users and c2 > 0) then
				list_of_node_pos_users = minetest.formspec_escape(table.concat(
								node_pos_users, ", "))
			end
		end
		additional_buttons = "button[11.4,1.9;2.5,0.9;show_var_usage;Where is it used?]"..
			"tooltip[show_var_usage;Show which NPC use this variable in which context.]"..
			-- offer a dropdown list and a text input field for new varialbe names for adding
			"label[0.2,3.05;Players with read access to this variable:]"..
			yl_speak_up.create_dropdown_playerlist(player, pname,
				pl_with_read_access,
				yl_speak_up.speak_to[pname].tmp_index_var_read_access,
				5.5, 2.9, 0.0, "list_var_read_access", "player", "Remove player from list",
				"grant_player_var_read_access",
					"Enter the name of the player that shall\n"..
					"have read access to this variable.",
				"revoke_player_var_read_access",
					"If you click here, the selected player\n"..
					"will no longer be able to add new\n"..
					"pre(C)onditions which read your variable."
			)..add_read_button..
			"label[0.2,4.05;Players with *write* access to this variable:]"..
			yl_speak_up.create_dropdown_playerlist(player, pname,
				pl_with_write_access,
				yl_speak_up.speak_to[pname].tmp_index_var_write_access,
				5.5, 3.9, 0.0, "list_var_write_access", "player", "Remove player from list",
				"grant_player_var_write_access",
					"Enter the name of the player that shall\n"..
					"have *write* access to this variable.",
				"revoke_player_var_write_access",
					"If you click here, the selected player\n"..
					"will no longer be able to *write* new\n"..
					"values into this variable."
			)..add_write_button..
			"label[0.2,5.05;Type of variable: "..
				-- show variable type
				minetest.colorize("#FFFF00",
					(yl_speak_up.get_variable_metadata(k_long, "var_type")
					 or "String/text or numerical value, depending on how you use it"))..
					".]"..
			"label[0.2,6.05;This variable is used by the following "..
				minetest.colorize("#FFFF00", tostring(c1)).." NPC:\n\t"..
				-- those are only n_id - no need to formspec_escape that
				minetest.colorize("#FFFF00", list_of_npc_users)..".]"..
			"label[0.2,7.05;This variable is used by the following "..
				minetest.colorize("#FFFF00", tostring(c2)).." node positions:\n\t"..
				-- those are only pos_to_string(..) - no need to formspec_escape that
				minetest.colorize("#FFFF00", list_of_node_pos_users)..".]"
	end
	return "size[16,8.5]"..
		"label[5.0,0.0;* Manage your variables *]"..
		"label[0.2,0.8;Note: Each variable will store a diffrent value for each player who "..
				"interacts with the NPC.\n"..
				"You can grant read and write access to other players for your "..
				"variables so that they can also use them as well.]"..
		"label[0.2,2.05;Your variables:]"..
		-- offer a dropdown list and a text input field for new varialbe names for adding
		yl_speak_up.create_dropdown_playerlist(player, pname,
			table_of_vars, yl_speak_up.speak_to[pname].tmp_index_variable,
			2.2, 1.9, 1.0, "list_var_names", "variable", "Delete selected variable",
			"add_variable_name",
				"Enter the name of the new variable you\n"..
				"want to create.",
			"delete_variable",
				"If you click here, the selected variable\n"..
				"will be deleted."
		)..
		additional_buttons..
		"button[0.0,0.2;1.0,0.6;back;Back]"..
		"button[6.0,8.0;1.0,0.6;back;Back]"
end