Well, that can hardly be called a feature, really its more a marketing term. The funny thing about good lens as regard to DOF is that the better corrected the lens, the more likely the lens will exhibit a typical DOF. To get a deeper DOF, ( as in Deep field lens ) a lens can employ several technique regarding optical design, but no particular trick on optical design can give you narrower DOF as lens in real world is always worse than theoretical, but by that, the DOF increase, not decrease.
What do happen is the change of acuteness and defining / resolving power when shift from the focusing plane to defocussing plane. Not the actual quantitative, but how it exhibit in image.
Selective focsuing in a typical fast lens or tele really mean the capability to place the focus at a specific plane. This can be achived with any lens, but usually in lens term that mean the lens exhibit a fairly high contrast and acuteness when in focus. This term had been and is used by Zeiss in such manner ( and many other Mfr too ) but again one must note that this is just a by product of how the lens can be employed, in a word a technique to employ the high contrast and acuteness, not by itself a specific feature. One can do the same with any other lens that do not exhibit such contrast and acuteness, just that it would be harder to judge the focus when viewing.
My wager on the matter is this is just marketing jargon to tell that this lens is good for such and easily employed for such.
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