Why doesn't mine report an error?

Question

//Only scalars can be used. I used an array later. Just learn it and you will get an error.

define('BIAO',array(1,2,3) );

echo BIAO; ---Result:Array

Answer 1

echo cannot print array

Answer 2

php7会报notice错 Notice: Array to string conversion in E:\phpstudyv8\WWW\a.php on line 4 Array