So while it's interesting academically to know what relative-position *should* do, in practice it has no utility because you'd never use it anyway.

I was under the impression relative positioning is needed for
properly aligned drop caps (left align the "D" at the vertical
stroke rather than the left edges of the serifs). But some
fiddling with text-indent and/or other margins/spaces might
be sufficient, although not as obvious for maintenance purposes.