<SpikeArrest name='SA-1'>
    <!-- Identifier: optional -->
    <Identifier ref='request.header.some-header-name'/>
    <!-- MessageWeight: optional, but only one -->
    <MessageWeight ref='request.header.weight'/>
    <MessageWeight ref='propertyset.foo.weight'/>
    <!-- Rate: required -->
    <Rate ref='context-variable-here'>30ps</Rate>
</SpikeArrest>
