=item B<Priority>: [low|below_normal|normal|above_normal|high]

Applies to B<execute>.

B<Priority> is optional.  Use it to set the priority of the target
process.  The environment variable, WEBJOB_PRIORITY, trumps the value
of this control when set.  No priority is set by default.

On UNIX platforms, the priority values listed above correspond to the
following priority levels:

    low .............. 20
    below_normal ..... 10
    normal ...........  0
    above_normal .....-10
    high .............-20

On WINX platforms, the priority values listed above correspond to the
following priority classes:

    low .............. IDLE_PRIORITY_CLASS
    below_normal ..... BELOW_NORMAL_PRIORITY_CLASS
    normal ........... NORMAL_PRIORITY_CLASS
    above_normal ..... ABOVE_NORMAL_PRIORITY_CLASS
    high ............. HIGH_PRIORITY_CLASS

Note: If the specified priority can't be set, the target process will
abort.

Note: If an environment variable is defined but exceeds the maximum
allowed length, it will be rejected.

