2020-03-26 21:49:00

1 files changed, 29 insertions, 1 deletions

diff --git a/doc/context/sources/general/manuals/luametatex/luametatex-math.tex b/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
index 7f77bbd6d..6ae648e34 100644
--- a/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
+++ b/doc/context/sources/general/manuals/luametatex/luametatex-math.tex
@@ -1096,7 +1096,35 @@ with in the engine). The full list of flags is given in the next table:
 \LL
 \stoptabulate
 
-The effect can depend on the font (and for Cambria one can use for instance \type {"16}).
+The effect can depend on the font (and for Cambria one can use for instance \type
+{"16}).
+
+Sometimes you might want to act upon the size of a delimiter, something that is
+not really possible because of the fact that they are calculated {\em after} most
+has been typeset already. In the following example the all|-|zero specification
+is the trigger to make a fake box with the last delimiter dimensions and shift.
+It's an ugly hack but its relative simple and not intrusive implementation has no
+side effects. Any other heuristic solution would not satisfy possible demands
+anyway. Here is a rather low level example:
+
+\startbuffer
+\startformula
+\Uleft  \Udelimiter 5 0 "222B
+\frac{\frac{a}{b}}{\frac{c}{d}}
+\Uright \Udelimiter 5 0 "222B
+\kern-2\fontcharwd\textfont0 "222B
+\mathlimop{\Uvextensible \Udelimiter 0 0 0}_1^2 x
+\stopformula
+\stopbuffer
+
+\typebuffer
+
+The last line, by passing zero values, results in a fake operator that has the
+dimensions of the previous delimiter. We can then backtrack over the (presumed)
+width and the two numbers become limit operators. As said, it's not pretty but it
+works.
+
+\getbuffer
 
 \subsection[mathacc]{Accent handling with \lpr {Umathaccent}}