`(margin left-margin)', the space is displayed in the left marginal
area, if it is `(margin right-margin)', it is displayed in the right
marginal area, and if LOCATION is `(margin nil)' the space is
`(margin left-margin)', the space is displayed in the left marginal
area, if it is `(margin right-margin)', it is displayed in the right
marginal area, and if LOCATION is `(margin nil)' the space is