6.5 Descriptor matching
A style can indicate default preferences for the kind of material that will suit it best. The user can override the style default by going into the media selection settings panel (Personalize -> Durations -> Details -> more). That option is set to Style preference by default. A style author uses the following functions to specify the default media selection preference for her style.
The style preferred bias towards faces is set to the given bias value. The bias can take a value in the range -1.0 to 1.0. Positive values indicate a preference for faces and negative values indicate a preference against faces. 0.0 pretty much means “I don’t care about faces”. When not set, it defaults to 0.0.
A style indicates a preference for material with a particular value of the motion descriptor - the target - which can take a value in the range 0.0 (meaning low motion or activity) to 1.0 (meaning high motion or activity). The strength of the preference is indicated by the bias value which can take any value in the range 0.0 to 1.0. Higher values of the bias indicate a stronger preference for content with the given motion target value. When not set, the bias value is 0.0 and target is 1.0.
Similar to motion-preference but applies to the brightness descriptor. The ranges and meaning of bias and target parameters is also the same as motion-bias. When not set, the bias is 0.0 and target is 1.0.