Set symbol-sort-key to initialise the symbol with.
<p> Sorts features in ascending order based on this value. Features with lower sort keys are drawn and placed first. When {@link PropertyFactory#iconAllowOverlap} or {@link PropertyFactory#textAllowOverlap} is `false`, features with a lower sort key will have priority during placement. When {@link PropertyFactory#iconAllowOverlap} or {@link PropertyFactory#textAllowOverlap} is set to `true`, features with a higher sort key will overlap over features with a lower sort key. </p>