box-tuple-cdata: review fixes

src/box/lua/tuple.cc

@@ -574,6 +574,7 @@ box_lua_tuple_init(struct lua_State *L)
 	/* export C functions to Lua */
 	luaL_newmetatable(L, tuplelib_name);
 	luaL_register(L, NULL, lbox_tuple_meta);
+	/* save Lua/C functions to the global variable (cleaned by tuple.lua) */
 	lua_setglobal(L, "cfuncs");
 	luaL_register_type(L, tuple_iteratorlib_name,
 			   lbox_tuple_iterator_meta);

src/box/lua/tuple.lua

@@ -38,6 +38,8 @@ ffi.metatype('struct tuple', {
     __gc = tuple_gc;
     __len = cfuncs.__len;
     __tostring = function(tuple)
+        -- Unpack tuple, call yaml.encode, remove yaml header and footer
+        -- 5 = '---\n\n' (header), -6 = '\n...\n' (footer)
         return yaml.encode(methods.totable(tuple)):sub(5, -6)
     end;
     __index = function(tuple, key)