In Author-it, a topic or a map content can be used within several publications according to different combinations of variant values. Fluid Topics needs to know that a group of publications were in fact from the same origin. This is used for example to cluster results in the search page. Two topics or maps that share the same value of clusterId (computed by the connector) will be considered as such.
Once results are clustered, Fluid Topics need a way to differentiate them, so it can prompt the user about what is in the cluster.
The clusterSelector field fulfills this role: it must contain the name of a variant that will be different for every topic/map with the same clusterId.