Porting/Glossary has : xs_apiversion (xs_apiversion.U): This variable contains the version of the oldest perl binary compatible with the present perl. perl.c:incpush() and lib/lib.pm will automatically search in $sitearch for older directories across major versions back to xs_apiversion. This is only useful if you have a perl library directory tree structured like the default one. See INSTALL for how this works. The versioned site_perl directory was introduced in 5.005, so that is the lowest possible value. Since this can depend on compile time options it is set by Configure. Other non-default sources of potential incompatibility, such as multiplicity, threads, ^^^^^^^ debugging, 64bits, sfio, etc., are not checked for currently, ^^^^^^ ? though in principle we could go snooping around in old Config.pm files. where the underlined points (at least) seem to be innacurate. Merijn ?Thread Next