diff --git a/lua/config/statusline.lua b/lua/config/statusline.lua
index 5937629..d65d7cb 100644
--- a/lua/config/statusline.lua
+++ b/lua/config/statusline.lua
@@ -8,6 +8,7 @@ end
 
 local function ime_state()
   if vim.g.is_mac then
+    -- ref: https://github.com/vim-airline/vim-airline/blob/master/autoload/airline/extensions/xkblayout.vim#L11
     local layout = vim.fn.libcall(vim.g.XkbSwitchLib, 'Xkb_Switch_getXkbLayout', '')
     if layout == '0' then
       return '[CN]'