metadata marker block

init.lua

@@ -23,6 +23,7 @@ dofile(MP .. "/util.lua")
 dofile(MP .. "/pointed.lua")
 dofile(MP .. "/pos.lua")
 dofile(MP .. "/data.lua")
+dofile(MP .. "/metadata.lua")
 
 dofile(MP .. "/mapblock.lua")
 

metadata.lua

@@ -0,0 +1,41 @@
+
+local function update_formspec(meta)
+    local group = meta:get_string("group")
+    -- TODO
+
+    meta:set_string("formspec", [[
+        size[10,8.3]
+        real_coordinates[true]
+        field[0.1,0.4;8.8,0.8;group;Group;]] .. group .. [[]
+        button_exit[9,0.4;0.9,0.8;set;Set]
+        list[context;main;0.1,1.4;8,1;]
+        list[current_player;main;0.1,3;8,4;]
+        listring[]
+    ]])
+end
+
+minetest.register_node("mapblock_lib:metadata", {
+	description = "Mapblock-lib metadata marker",
+	tiles = {"mapblock_lib_metadata.png^[colorize:#23c1cc"},
+    drawtype = "allfaces",
+    use_texture_alpha = "blend",
+    paramtype = "light",
+    paramtype2 = "facedir",
+    sunlight_propagates = true,
+	groups = {
+		oddly_breakable_by_hand = 3
+	},
+
+	on_construct = function(pos)
+		local meta = minetest.get_meta(pos)
+        update_formspec(meta)
+	end,
+
+    on_receive_fields = function(pos, _, fields)
+        if fields.set then
+            local meta = minetest.get_meta(pos)
+            meta:set_string("group", fields.group)
+            update_formspec(meta)
+        end
+    end
+})