+ >*NOTE:*
+ v4.x will be PHP-8 only, v3.x continues PHP-7 support
+
+ * PHP 8 compatibility
+ - Drop ext-propro support
+ PHP 8 removes the object get/set API from the ZendEngine, which renders
+ that extension dysfunctional. As a consequence, the header property of
+ http\Message and derived classes cannot be modified in place, and thus
+ by reference.