diff --git a/README.md b/README.md
index 43d3d70..e1160c7 100644
--- a/README.md
+++ b/README.md
@@ -607,5 +607,38 @@ function source:execute(completion_item, callback)
   callback(completion_item)
 end
 
-return source
+require('cmp').register_source(source.new())
+```
+
+You can also create source by Vim script like this (This is useful to support callback style plugins).
+
+- If you want to return `boolean`, you must return `v:true`/`v:false`. It doesn't `0`/`1`.
+
+```vim
+let s:source = {}
+
+function! s:source.new() abort
+  return extend(deepcopy(s:source))
+endfunction
+
+" The other APIs are also available.
+
+function! s:source.complete(params, callback) abort
+  call a:callback({
+  \   { 'label': 'January' },
+  \   { 'label': 'February' },
+  \   { 'label': 'March' },
+  \   { 'label': 'April' },
+  \   { 'label': 'May' },
+  \   { 'label': 'June' },
+  \   { 'label': 'July' },
+  \   { 'label': 'August' },
+  \   { 'label': 'September' },
+  \   { 'label': 'October' },
+  \   { 'label': 'November' },
+  \   { 'label': 'December' },
+  \ })
+endfunction
+
+call cmp#register_source('month', s:source.new())
 ```
diff --git a/lua/cmp/core.lua b/lua/cmp/core.lua
index 612fabb..b7b8454 100644
--- a/lua/cmp/core.lua
+++ b/lua/cmp/core.lua
@@ -307,7 +307,6 @@ core.confirm = function(e, option, callback)
     table.insert(restore, keymap.t(string.rep('<C-g>U<Left><Del>', vim.fn.strchars(e:get_word()))))
     table.insert(restore, string.sub(e.context.cursor_before_line, e:get_offset()))
     keymap.feedkeys(table.concat(restore, ''), 'n', function()
-
       --@see https://github.com/microsoft/vscode/blob/main/src/vs/editor/contrib/suggest/suggestController.ts#L334
       if #(misc.safe(e:get_completion_item().additionalTextEdits) or {}) == 0 then
         local pre = context.new()
diff --git a/lua/cmp/vim_source.lua b/lua/cmp/vim_source.lua
index 90f938b..a991b85 100644
--- a/lua/cmp/vim_source.lua
+++ b/lua/cmp/vim_source.lua
@@ -11,7 +11,7 @@ end
 ---@param callback function
 ---@return number
 vim_source.to_callback = setmetatable({
-  callbacks = {}
+  callbacks = {},
 }, {
   __call = function(self, callback)
     local id = misc.id('cmp.vim_source.to_callback')
@@ -20,7 +20,7 @@ vim_source.to_callback = setmetatable({
       self.callbacks[id] = nil
     end
     return id
-  end
+  end,
 })
 
 ---Convert to serializable args.
@@ -36,7 +36,7 @@ end
 
 ---@param id number
 ---@param methods string[]
-vim_source.new = function (bridge_id, methods)
+vim_source.new = function(bridge_id, methods)
   local self = {}
   for _, method in ipairs(methods) do
     self[method] = (function(m)
@@ -49,4 +49,3 @@ vim_source.new = function (bridge_id, methods)
 end
 
 return vim_source
-