From 4bc28891615011ed3581836e9259434720e25830 Mon Sep 17 00:00:00 2001
From: Hans Hagen <pragma@wxs.nl>
Date: Thu, 4 Jul 2019 13:50:48 +0200
Subject: 2019-07-04 12:36:00

---
 doc/context/sources/general/manuals/bidi/bidi.tex | 41 ++++++++++++-----------
 1 file changed, 21 insertions(+), 20 deletions(-)

(limited to 'doc/context/sources/general/manuals/bidi/bidi.tex')

diff --git a/doc/context/sources/general/manuals/bidi/bidi.tex b/doc/context/sources/general/manuals/bidi/bidi.tex
index abd3f64fa..fb3705a37 100644
--- a/doc/context/sources/general/manuals/bidi/bidi.tex
+++ b/doc/context/sources/general/manuals/bidi/bidi.tex
@@ -461,38 +461,39 @@ We assume that you run \CONTEXT\ \MKIV\ in combination with \LUATEX. Direction
 support in this engine has been improved over time. Originally the \OMEGA\
 (\ALEPH) direction model was used but in the meantime it has been stripped to the
 basics, and what used to be so called whatsits (extension nodes) are now first
-class nodes. In the \LUA\ interface we still support the:
-
-\startitemize[packed]
-\startitem
-    \type {TLT} and \type {TRT} keywords for local par nodes
-\stopitem
-\startitem
-    \type {+TLT}, \type {-TLT}, \type {+TRT} and \type {-TRT} keywords for
-    direction nodes
-\stopitem
-\stopitemize
-
-However, because we use dedicated nodes, and because nodes actually store numbers
-and not strings we also expose the numeric model:
+class nodes. Of the many directions only four are kept in \LUATEX\ and they are
+indicated by three letters:
 
 \starttabulate[|l|l|l|]
 \NC 0 \NC \type {TLT} \NC left to right \NC \NR
 \NC 1 \NC \type {TRT} \NC right to left \NC \NR
-\NC 2 \NC \type {LTL} \NC not used in context \NC \NR
-\NC 3 \NC \type {RTT} \NC not used in context \NC \NR
+\NC 2 \NC \type {LTL} \NC not used in context (obsolete) \NC \NR
+\NC 3 \NC \type {RTT} \NC not used in context (obsolete) \NC \NR
 \stoptabulate
 
-These values are used for local par nodes as well as direction nodes. In addition
-a direction node has a subtype:
+In \LUAMETATEX, and therefore \CONTEXT\ \LMTX\ we only have the first two.
+Therefore in \LMTX\ you normally don't have to worry about checking for them at
+the \LUA\ end because they are irrelevant for calculations (the vertical ones
+swapped the horizontal and vertical progression). Also, when really needed, we
+use the \type {direction} keys with numerical indicators, so zero for \type {l2r}
+and one for \type {r2l}. These values are used for local par nodes as well as
+direction nodes. In addition a direction node has a subtype:
 
 \starttabulate[|l|l|l|]
 \NC 0 \NC \type {normal} \NC comparable to \type {+} \NC \NR
 \NC 1 \NC \type {cancel} \NC comparable to \type {-} \NC \NR
 \stoptabulate
 
-The \type {dir} field uses the strings, the \type {direction} field the number
-(both of course share the same internal node variable).
+\stopchapter
+
+\startchapter[title={Going vertical}]
+
+Normally the term bidi is reserved for horizontal direction swapping but there is
+no reason to limit our view to that. So, here I will spend some words on how we
+can deal with vertical directions.
+
+{\em I will move some (not yet public) explanation from elsewhere to here in due
+time.}
 
 \stopchapter
 
-- 
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