* The PRI_MINIMUM priority is a value less than any practical
* priority value, it is used when compare between different
* priority values.
*
* The PRI_AFTERMODIFY priority represents the notification will be
* sent after any internal modification has finished.
*
* The PRI_BEFOREMODIFY priority represents the notification will be
* sent before any internal modification happens.
*
* So an element mark with PRI_BEFOREMODIFY will be handled first,
* and one with PRI_AFTERMODIFY will be handled at last.