The Relevance option applies the most relevant metadata key value for the current search.
For example, an "Introduction" topic exists in a document named "Installation guide". This guide exists in three versions: 1.0, 1.1, and 2.0. There are three versions of the topic.
By selecting the Relevance option, when users search Introduction Installation guide 2.0, the 2.0 version of the topic appears first in the switch to relatives.