Most transcoding actions rely and define a few global constants, typically:

 define('DEFAULT_MOBILE_DEVICE_NAME', 'is_wireless_device');
 define('DEFAULT_MOBILE_DEVICE_NAMESPACE', TranscodingAction::$WURFL_VOCABULARY);
 define('DEFAULT_MOBILE_DEVICE_ASPECT', '__NULL');
 define('DEFAULT_MOBILE_DEVICE', true);

Things at the common library level should not define and/or rely on global constants being defined because there is no way to ensure unique names will be used, and that, e.g. the library won't be used in a project where DEFAULT_PERCENT means something completely different from its meaning for TranscodingActionPagination.

Global constants should be replaced by class constants everywhere (I think they work starting with PHP5, but that may need to be confirmed):
 http://fr2.php.net/manual/en/language.oop5.constants.php