/// * Compute a custom score by the subQuery score and a number of
/// ValueSourceQuery scores.
///
/// Subclasses can override this method to modify the custom score.
///
/// If your custom scoring is different than the default herein you
/// should override at least one of the two customScore() methods.
/// If the number of ValueSourceQueries is always < 2 it is
/// sufficient to override the other
/// CustomScore()
/// method, which is simpler.
///
/// The default computation herein is a multiplication of given scores:
///
/// ModifiedScore = valSrcScore * valSrcScores[0] * valSrcScores[1] * ...
///
///
///