me@host> perl -c XXA.pm 
Beginning XXA compile
  Beginning XXB compile
    Beginning XXA compile
      Just used XXB in XXA compile
Bareword "xxb" not allowed while "strict subs" in use at XXA.pm line 26.
BEGIN not safe after errors--compilation aborted at XXA.pm line 29.
BEGIN failed--compilation aborted at XXB.pm line 15.
BEGIN failed--compilation aborted at XXA.pm line 15.
me@host:>