The Perl documentation is somewhat thin on advice to module installers and module authors wrt (non-)pollution and what to do about it. INSTALL warns about the issue and tells about the POLLUTE flag. But this file typically won't be around when modules are being installed. And in any case it's hardly an obvious place to look. The same information is in the documentation of MakeMaker, but only if you know where to look. (This is part of a more general problem - lots of information relevant to module installers is only to be found in the MakeMaker pod. "perllocal.pod" has recently been highlighted.) There's also an entry in perldelta, but again, why would a module installer look there? Presumably there needs to be a paragraph in perlmodinstall. And for module authors, there's no advice at all. What is the recommended way that authors should upgrade their modules, so that they are installable with current Perls and also with older ones? Is the best approach to a) change all relevant symbols from xxxx to PL_xxxx b) for each symbol used, insert #ifndef PL_xxxx # define PL_xxxx xxxx #endif Assuming that is the appropriate advice, where should it be put? Mike GuyThread Next