Another one that's false is a list of undefs. An array of undefs though is true.

   if ( (undef,undef) ) { }   # a list of undefs is false

   @arr = (undef,undef);
   if ( @arr ) {}             # an array of undefs is true
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We make use of this like so:

   $_ = 'x';
   if (($a,$b) = m/(.)(.)/) { }
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mc0e