From 36355f3d0c23357fccf2c76b3e9605a41cae519d Mon Sep 17 00:00:00 2001
From: Hans Hagen <pragma@wxs.nl>
Date: Wed, 21 Dec 2022 18:00:37 +0100
Subject: 2022-12-21 17:12:00

---
 .../general/manuals/lowlevel/lowlevel-boxes.tex    | 32 ++++++++++++++++++++
 .../manuals/lowlevel/lowlevel-registers.tex        | 35 +++++++++++++++++++++-
 .../general/manuals/luametatex/luametatex.tex      |  4 ---
 3 files changed, 66 insertions(+), 5 deletions(-)

(limited to 'doc/context')

diff --git a/doc/context/sources/general/manuals/lowlevel/lowlevel-boxes.tex b/doc/context/sources/general/manuals/lowlevel/lowlevel-boxes.tex
index d5105fc8c..dd6c2f2d4 100644
--- a/doc/context/sources/general/manuals/lowlevel/lowlevel-boxes.tex
+++ b/doc/context/sources/general/manuals/lowlevel/lowlevel-boxes.tex
@@ -689,6 +689,38 @@ test\quad
 \ruledhbox{\getbuffer}
 \stoplinecorrection
 
+Where a \type {\vtop} has the baseline at the top, a \type {\vbox} has it at the
+bottom. In \LUAMETATEX\ we also have a \type {\dbox}, which is a \type {\vbox} with
+that behaves like a \type {\vtop} when it's appended to a vertical list: the height of
+the first box or rule determines the (base)line correction that gets applied. The following
+example demonstrates this:
+
+\startlinecorrection
+\startcombination [nx=3,ny=1,location=top]
+    {\vbox \bgroup \hsize .3\textwidth
+        \small\small \setupalign[tolerant,stretch] \dontcomplain
+        xxxxxxxxxxxxxxxx\par
+        \ruledvbox{\samplefile{tufte}}\par
+        xxxxxxxxxxxxxxxx\par
+     \egroup} {\type {\vbox}}
+    {\vbox \bgroup \hsize .3\textwidth
+        \small\small \setupalign[tolerant,stretch] \dontcomplain
+        xxxxxxxxxxxxxxxx\par
+        \ruledvtop{\samplefile{tufte}}\par
+        xxxxxxxxxxxxxxxx\par
+     \egroup} {\type {\vtop}}
+    {\vbox \bgroup \hsize .3\textwidth
+        \small\small \setupalign[tolerant,stretch] \dontcomplain
+        xxxxxxxxxxxxxxxx\par
+        \ruleddbox{\samplefile{tufte} }\par
+        xxxxxxxxxxxxxxxx\par
+     \egroup} {\type {\dbox}}
+\stopcombination
+\stoplinecorrection
+
+The \type {d} stands for \quote {dual} because we (sort of) have two baselines. The
+regular height and depth are those of a \type {\vbox}.
+
 \stopsectionlevel
 
 \stopdocument
diff --git a/doc/context/sources/general/manuals/lowlevel/lowlevel-registers.tex b/doc/context/sources/general/manuals/lowlevel/lowlevel-registers.tex
index 4dbee67cd..233a8c178 100644
--- a/doc/context/sources/general/manuals/lowlevel/lowlevel-registers.tex
+++ b/doc/context/sources/general/manuals/lowlevel/lowlevel-registers.tex
@@ -245,7 +245,40 @@ better use the proper more high level definers (not discussed here).
 
 \startsectionlevel[title={\LUAMETATEX\ primitives}]
 
-{\em todo}
+The fact that scanning stops at a non-number or \type {\relax} can be sort of
+unpredictable which is why in \LUAMETATEX\ we also support the following variant:
+
+\starttyping[option=TEX]
+\scratchdimen\dimexpr  10pt + 3pt \relax
+\scratchdimen\dimexpr {10pt + 3pt}
+\stoptyping
+
+At the cost of one more token braces can be used as boundaries instead of the
+single \type {\relax} boundary.
+
+An important property of registers is that they can be accessed by a number. This
+has big consequences for the implementation: they are part of the big memory
+store and consume dedicated ranges. If we had only named access \TEX's memory
+layout could be a bit leaner. In principle we could make the number of registers
+smaller because any limit on the amount at some point can be an obstacle. It is
+for that reason that we also have name-only variants:
+
+\starttyping[option=TEX]
+\dimensiondef \MyDimenA   12pt
+\integerdef   \MyIntegerA 12
+\gluespecdef  \MyGlueA    12pt + 3pt minus 4pt
+\mugluespecdef\MyMuA      12mu + 3mu minus 4mu
+\stoptyping
+
+These are as efficient but not accessible by number but they behave like
+registers which means that you (can) use \type {\the}, \type {\advance}, \type
+{\multiply} and \type {\divide} with them. \footnote {There are also the slightly
+more efficient \type {\advanceby}, \type {\multiplyby} and \type {\divideby} that
+don't check for the \type {by} keyword.} In case you wonder why there is no
+alternative for \type {\toksdef}, there actually are multiple: they are called
+macros.
+
+{\em todo: expressions}
 
 \stopsectionlevel
 
diff --git a/doc/context/sources/general/manuals/luametatex/luametatex.tex b/doc/context/sources/general/manuals/luametatex/luametatex.tex
index 96f700355..ba19d58e1 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex.tex
@@ -21,10 +21,6 @@
 % clang bins are still slower .. quite inconsistent differences between 32 and
 % 64 bit (not all compilers are the same version)
 
-% \loggingall
-% \tracingonline    \zerocount
-% \tracingmacros    \plusone
-
 % \enableautoglyphscaling % saves only a few instances ... no gain .. a few pages more
 
 % \enabletexdirective{vspacing.experimental}
-- 
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