question about Ext2/3 append-only attributes

[Xin Zhao <uszhaoxin@gmail.com>]

I read some specification says that if append-only is set to a
directory, you can only create or modify files in that directory, but
no delete.

But when I tried this attribute on a directory,  I was not able to
create new files in that directory.  let's say the derectory is /dev, 
I set it to be append-only with:

chattr +a /dev.

Then I cannot create new files in it with command cp /dev/aa /dev/bb,
not that aa is a normal text file here.

Why the result conflict with the specification? Is there anyway to
make a directory really append-only? Thanks in advance!

-x