Z:gnu-www-ja-netscape-npl--475f11-The NPL has the form of a copy/en

The NPL has the form of a copyleft; it explicitly says that all modifications made by users must be released under the NPL. But this applies only to modifications to the existing code&mdash;not to added subroutines, if they are put in separate files. As a practical matter, this means it is easy to make proprietary changes if you want to: just put the bulk of your code into a separate file, and call the collection a Larger Work. Only the subroutine calls added to the old files will have to be released under the NPL, and they will not be very useful on their own.