Is There A System Defined Environment Variable For Documents Directory?

I know about the %USERPROFILE% system defined environment variable on Windows XP (and Vista and Windows 7). Is there a system defined environment variable pointing to the location of the "My Documents" directory? On XP by default it's %USERPROFILE%\My Documents and on Win 7 it's %USERPROFILE%\Documents. I just wanted to avoid having to test for the OS version in a Powershell script if I can avoid it.