Perl development has four major aims: extending portability, fixing bugs, optimizations, and adding language features. Patches to Perl are usually made against the latest copy of the development release; the very latest copy, stored in the Perl repository (see Section 2.5 below) is usually called `bleadperl'.
The bleadperl eventually becomes the new minor release, but patches are also picked up by the maintainer of the stable release for inclusion. While there are no hard and fast rules, and everything is left to the discretion of the maintainer, in general, patches which are bug fixes or address portability concerns (which include taking advantage of new features in some platforms, such as large file support or 64 bit integers) are merged into the stable release as well, whereas new language features tend to be left until the next minor release. Optimizations may or may not be included, depending on their impact on the source.