[Puppet Users] Managing the Puppet type "user"

My question is about using

resources { 'user':
purge => true,
}

On http://docs.puppetlabs.com/references/stable/type.html#resources it mentions a parameter "unless_system_user" :

"This keeps system users from being purged. By default, it does not purge users
whose UIDs are less than or equal to 500, but you can specify a different UID
as the inclusive limit. Valid values are true, false. Values can match /^\d+$/."

Are the following examples valid ? !! with the understanding that only ONE would be used !!

# the first two are obvious, but I prefer to have the examples
resources { 'user':
purge => true,
unless_system_user => false,
}

resources { 'user':
purge => true,
unless_system_user => true,
}

# this is the REAL question
resources { 'user':
purge => true,
unless_system_user => '1000',
}

“Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us.”
Bill Waterson (Calvin & Hobbes)