> There is no way to know what part of a web site has or 
> has not changed.

If u browse a website frequently, u should have know which part is updated,
isn't it?Or I just want certain part to be updated, and retain all other parts
structure at the same time, tis is what called an "update".

Let say u're running a movie website, ur website contains several
sub-directories to categorize all the movies' genres which go like this
www.movie.com/genres/comedy
www.movie.com/genres/horror
www.movie.com/genres/sci-fic
www.movie.com/genres/action
.
.
.
U hav got some movies to be updated into the "horror" today, will you delete
all others for just tis update? 
U won't b'coz it doesn't make sense at all, isn't it?same thing applies to
httrack. 
Httrack update is just like performing a whole new ripping project instead of
"Update", if u know what i mean......

> No where: <http://www.httrack.com/html/step9_opt5.html> 
> Do not purge old files.
> (But remember they will not be linked into the mirror)

It would be good to have the old files retained as well as the structure at
the same time, tis is wat an "Update" should be looked like.