Thanks for the pointer. I've taken a look at the chapter on versions. This is full of useful information, but doesn't really address my query; it is listing new features and suggesting ways they might be used, rather than pointing out possible pitfalls. It doesn't mention the CHECK keyword introduced in Perl 5.6 for example.

Nevertheless this looks like an invaluable source for Perl information and one I'm sure I'll refer to in the future.

Thanks again,

Roger