Also, IIRC, the strict and warning pragma's are imported *after* the BEGIN block.

There's one way to find out :)

$ perl   
use strict;
BEGIN { $x = 'y'; $$x = 1; print $y }
Global symbol "$x" requires explicit package name at - line 2.
Global symbol "$x" requires explicit package name at - line 2.
Global symbol "$y" requires explicit package name at - line 2.
BEGIN not safe after errors--compilation aborted at - line 2.
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As it turns out, use calls reduce to BEGIN blocks and BEGIN blocks fire in order of encountering.

A BEGIN block is not marked by the sub keyword. Instead, you just use BEGIN {...}

It can be, though. "sub BEGIN" doesn't create a normal sub called BEGIN, but it is valid syntax. In fact, it is how B::Deparse deparses BEGIN blocks. The same goes for CHECK, INIT and END. See also what perlmod has to say about this.