pub unsafe static kMDQueryResultContentRelevance: Option<&'static CFString>MDQuery only.Expand description
The name of a query-specific attribute for use in sorting. The relevance of an item is a CFNumberRef with a floating point value. This is the relevance for content searches. The maximum and minimum values for a particular search cannot be determined until all of the results have been returned. If there are multiple kMDItemTextContent predicates in the query, no relevance is returned. This is an attribute of a result item that is specific to the item in the context of the query. Also, the relevance does not compare the result relative to the other results of a query, but is computed just on the result item itself. Finally, this is only the relevance value for content, not a relevance for the item as a whole. The relevance attribute may not even be computed for an item if the item is found to match the query through evaluation of other attributes of the item than its contents. If the value is not computed, it is treated as an attribute on the item which does not exist (for sorting purposes, for example).
See also Apple’s documentation