[Zope] LocalFS Overwrite local files option

[Anclo]

I want to protect image files in a LocalFS directory so they could not be 
deleted or overwritten, so I disallowed the options Delete local files, 
Delete objects, and Overwrite local files.

But what does the option Overwrite local files really do? Zope does not let 
me create 2 objects with the same ID whether this option is on or off.

Thanks,

Anclo