Description:
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The __construct() method on SimpleXMLElement is marked 'final', which prevents extension of the class for, say, XML-format-specific objects which augment otherwise empty incoming XML data.

The current workaround is to use __get and __set and company (which unfortunately means <?= $obj instanceof SimpleXMLElement ?> fails), and which is much slower -- or to use a static factory method which forces some XML in there (which is syntactically ugly imo.)

Not to shoot my request in the foot, but I forsee possible issues with these functions:

- simplexml_import_dom ( $node [, $class_name ] )
- simplexml_load_file ( string $filename [, string $class_name ] ... )
- simplexml_load_string ( string $data [, string $class_name ] ... )

However, perhaps it would suffice to require 'a compatible function signature' rather than to mark it final?