What is the maximum possible priority value of an xfrm policy in linux?

      ip xfrm policy { deleteall | list } [ dir DIR ] [ SELECTOR ] [ index INDEX ]
                    [ action ACTION ] [ priority PRIORITY ]

The man page talks about the default value, but not about the minimum and maximum values.

priority PRIORITY
             priority is a number. Default priority is set on zero.

Can someone please let me know what their minimum and maximum values are and which header file I can find them in?

As @Blabbo the Verbose mentioned in comments:

• The highest priority is 0 (default)
• The lowest priority is 4,294,967,295 (the maximum uint32_t value).