PHP doesn’t fail if two define statements assign a value to the same constant name: in such a case, PHP only issues a warning and
ignores the second define. However, that code should be fixed. In the best case, the second define tries to assign the same
value to the constant: it’s just useless code which can be removed. In the worst case, the second define attempts to assign a different
value and is followed by code which wrongly assumes the value of the constant: it can be a nasty bug.
Noncompliant Code Example
define( 'WP_DEBUG', 1 );
define( 'SCRIPT_DEBUG', 1 );
define( 'WP_DEBUG', 0 ); // Noncompliant, redefines constant defined 2 lines above
echo WP_DEBUG; // output "1"
