Many thanks, Hans. The method appears to work only for nbsp, not zwj etc. Here is the updated MWE:
=======
\startTEXpage[offset=1em]
\disabletrackers[typesetters.directions]
\disabletrackers[typesetters.zwj]
\disabletrackers[typesetters.zwnj]
\disabletrackers[typesetters.nbsp]
\definedfont[almfixed at 14pt]
ZWJ:
ZWNJ:
NBSP:
\stopTEXpage
=======
See attached, please advise.
joiners are part of replacement etc and can come and go ... they are
characters (we could visualize them but one never knows for sure if one
sees them)
nbsp are spaces and become glue that we can trace reliable in the node list
Many thanks. Ok, here is another MWE featuring a workaround using fallbacks:
==============
\definefontfallback[nosymbols] [file:lmmono10-regular] [200C,200D] [force=yes]
\starttypescript [serif] [alm] [name]
\definefontsynonym [Serif] [ArabicLatinSerif]
\stoptypescript
\starttypescript [mono] [alm] [name]
\definefontsynonym [Mono] [ArabicLatinMono]
\stoptypescript
\starttypescript [serif] [alm]
\definefontsynonym [ArabicLatinSerif] [file:almfixed] % [fallbacks=nosymbols]
\stoptypescript
\starttypescript [mono] [alm]
\definefontsynonym [ArabicLatinMono] [file:almfixed] [fallbacks=nosymbols]
\stoptypescript
\starttypescript [almfixed-nosymbols]
\definetypeface [\typescriptone] [rm] [serif] [alm] [default]
\definetypeface [\typescriptone] [tt] [mono] [alm] [default]
\stoptypescript
\usetypescript[almfixed-nosymbols]
\setupbodyfont[almfixed-nosymbols,12pt]
\startTEXpage[offset=1em]
\rm
ZWJ:
ZWNJ:
NBSP:
\tt
ZWJ:
ZWNJ:
NBSP:
\stopTEXpage
==============
Under \rm we get the symbols, and under \tt they are suppressed. Of course it doesn't matter what fallback font one uses, as long as it has no control-character symbols.
1. Can this approach be generalized to get what we want, viz., a way to toggle the symbols?
2. \enabletrackers[typesetters.nbsp] gives a colored box, which is at least something.. But how can we get the NBSP symbol that's alerady in the font?
3. Ideally:
a. we want all Unicode control symbols to show up in verbatim or in \typebuffer (as in a text editor);
b. we want all Unicode control symbols to be suppressed in final pdf output (for, e.g., printing).
But some fonts meant for printing have symbols for Unicode control chars -- that poses a challenge.
And some fonts meant for verbatim/editing do not have symbols for the control chars -- that also poses a challenge. AlmFixed, of course, has them.
Most minimally decent Arabic fonts have symbols for the Unicode control chars as default, including Scheherazade, Amiri, Uthmanic, and Noto Naskh Arabic -- all free fonts.
Industry workhorses like Linotype Lotus (Arabic) also have them.
Uniscribe applications like Notepad/Word allow for toggling in a WYSIWYG context -- can't speak for HarfBuzz -- so there is no harm in having explicit symbols in the font.
The upshot is that, for non-Latin scripts, some toggling capability in ConTeXt is important to have -- even inescapable for Arabic-script piblishing.
Perhaps others who use Arabic-script or Indic, etc., can chime in.. Am hopeful that we can figure something out!
Best wishes
Idris