The desc.C file should not be modified manually.  Please use dtstyle
to make any modifications.  The format of desc.C is very sensitive.
When you make changes using dtstyle, the saved changes will be in
$HOME/.dt/webbackdrops directory.  So the best way to make global
changes for all users to see is to use dtstyle to make the changes,
and then concatenate the modified $HOME/.dt/webbackdrops/desc.webbackdrops
with /etc/dt/webbackdrops and put the newly created file in 
/var/dt/webbackdrops.

Although this code is shipped here today, it has not yet been 
enabled.  We hope to enable Web Backdrops some time in the
future.