'Here Maps 'segmentRef' attribute explanation

Can someone explain/point to documentation that explains the 'segmentRef' attribute that gets returned by the Here Routing API v8 when spans="segmentRef". An example of what gets returned is shown below. The middle part seems to be the topologyID but I can't figure out the rest. Thanks.

$0:321534451:$1:457679505#-0..0.7675126869621484


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