[XeTeX] \predisplaydirection primitive from etex

[Jonathan Kew]

On Mon, Apr 5, 2010 at 4:52 PM, Vafa Khalighi <vafakh84 at gmail.com> wrote:

> 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?
>
>
Well, I've never used this, but a little experimentation indicates that it
seems to do just what the doc says; see attached. Note that there also
appears to be a spacing bug associated (see the last example).

JK
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