deprecated modules and features

Deprecated modules and features are those which were part of a stable release, but later found to be subtly flawed, and which should be avoided. They are subject to removal and/or bug-incompatible reimplementation in the next major release (but they will be preserved through maintenance releases). Deprecation warnings are issued under -w or use diagnostics, and notices are found in perldeltas, as well as various other PODs. Coding practices that misuse features, such as my $foo if 0, can also be deprecated.