I found a description in CCSprite9Slice's document.
maginBottom
Sets the bottom margin exclusively.
http://www.cocos2d-swift.org/docs/api/Classes/CCSprite9Slice.html
I couldn't figure out what "exclusively" means. Is there difference without it.
Maybe this is a simply English question, but I think this is related programming.
I believe the class reference used the word "exclusively" incorrectly. Perhaps this should have been phrased "Sets the bottom margin separately from the other margins."
Because there's a global margin property that sets the margin to all four borders to the same value, it can be safely assumed that "separately" is what the property description intended to say.