[Zope] Question of ZPL etiquette

[David Pratt]

Hi. I am trying to get a better sense of how others are dealing with ZPL 
headers in code from original authors once changes are made. For example 
if a package is ZPL copyright somebody, I typically see a header at the 
top of most files as well as the LICENSE.txt in the package itself. When 
changes are made however, it is typical see headers replaced with the 
header of the author(s) who have made changes and date. A second license 
will now apply to the modified package with the ZPL license of the 
original code left to acknowledge authors and copyright of the original 
product/package. Is that a fair assessment? Is that generally 
acceptable? Many thanks.

Regards,
David