[OS X TeX] Preview.app adds auto refresh function (partial) in 10.5.3?

[Di Xiao]

Hi,

In 10.5.3, open a PDF generated by TeX using Preview.app.  Edit the
source file, compile, and bring Preview.app to front.  The PDF will be
automatically updated once Preview.app gains focus.  However, if it
stays in the background, the auto update won't happen.

I'm not sure if this function is introduced in 10.5.3 or earlier
because I just find it now.

-- D.