[pdftex] \predisplaydirection primitive from etex

[Vafa Khalighi]

This is a very useful primitive that I just found now.
http://tex.loria.fr/moteurs/etex_ref.html#predisplaydirection says:

"an internal read/write integer, initialised by e-TeX to indicate the
direction of the last partial paragraph before a display; it is used to
control the placement of elements such as equation numbers, and can be
explictly set to affect this placement. "

But whatever integer, I give to this primitive, I see no difference. Could
please someone send a minimal document showing how this primitive actually
works?

Thanks

-- 
Best wishes,
Vafa Khalighi
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