Consider the following almost-minimal example:
\setuptagging [state=start]
\setuppapersize [A6]
\setupexternalfigures[location=default]
\definemakeup [cover4][page=left,doublesided=no]
\definelayer [isbn][width=\pagewidth,height=\pageheight]
\define \Title {A Primer on Omphaloskepsis}
\startsetups [placeisbn]
\setlayer [isbn][preset=rightbottom,hoffset=5mm,voffset=5mm]
{\externalfigure[cow.pdf][width=3cm]}
\stopsetups
\starttext
\setupbackgrounds [page][setups=placeisbn,background=isbn]
\startmakeup [cover4]
\scale [width=\textwidth] {\red \Title}
\stopmakeup
\stoptext
For me (Win64, current standalone beta), compilation halts with:
lua error > lua error on line 4 in file
C://Users/rik/Desktop/xxx.tex:
...ext/tex/texmf-context/tex/context/base/mkiv/back-exp.lua:823:
attempt to index local 'spec' (a nil value)
stack traceback:
...ext/tex/texmf-context/tex/context/base/mkiv/back-exp.lua:823: in
function <...ext/tex/texmf-context/tex/conte
xt/base/mkiv/back-exp.lua:818>
(It always points to line 4 of the file, no matter the file.) When the
halt is answered with a CR, the processing runs to completion with no
apparent errors.
When the first line is removed, or the state set to stop, compilation
completes normally.
When the content of the setup (the two-line \setlayer) is moved out of
the setup, compilation completes normally (without regard to tagging).
(I use a setup here because, in the real work on which this is based,
there are other items in the layer that cannot be properly handled until
after \starttext processing.
--
Rik
