Win Form DataDirectory

Where is DataDirectory ?
ADO.NET |DataDirectory| where is this documented?
使用DataDirectory---WinForm程序中兩份mdf文件問題的解決

var path = AppDomain.CurrentDomain.BaseDirectory;
var startPath = Application.StartupPath;
var dataPath = Environment.GetFolderPath(
               Environment.SpecialFolder.CommonApplicationData);

AppDomain.CurrentDomain.SetData("DataDirectory", dataPath);