Can now control closing for formspec

API.md

@@ -46,6 +46,10 @@ This has the function signature `callback(playername, itemstring)`.
 * `playername` is the name of the player who selected the item,
 * `itemstring` is the itemstring of the chosen item.
 
+Normally, if the player pushes a button, the formspec is closed.
+But if you return `false` in this callback, the formspec is *not*
+Use this when you run into problems.
+
 ## Examples
 Display all items from Creative inventory to player 1:
 ```

init.lua

@@ -155,9 +155,15 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 			end
 		end
 		if item then
-			minetest.close_formspec(playername, formname)
+			local close = true
 			for i=1,#callbacks do
-				callbacks[i](playername, item)
+				local ret = callbacks[i](playername, item)
+				if ret == false then
+					close = false
+				end
+			end
+			if close then
+				minetest.close_formspec(playername, formname)
 			end
 			reset_player_info(playername)
 		end