BEGIN {
  *old_import = \&import
    if defined &import;
}
sub import {
  _init(@ISA);
  goto &old_import
    if defined &old_import;
}
sub _init {
  foreach(@_) {
    _init(@{$_."::ISA"}) if exists ${$_.'::'}{ISA};
    *{$_."::define_attributes"} = \&define_attributes
      unless defined &{$_.'::define_attributes'};
  }
}