Found the origin of the curious error message containing my name.
Comes from the inclusion of a file named type-loc.mkiv residing in a directory ~/TeX/texmf/tex/context/user/ and containing:

\endinput

Op NTG ConTeXt nieuwsgroep, antwoord van Hans Hagen.

On 1/3/2014 2:33 PM, H. van der Meer wrote: (etc.)

How this got included? I have no idea.
But removing it did not make a difference, even after calling mtxrun --generate.


On 10 Jun 2019, at 22:21, Hans van der Meer <havdmeer@ziggo.nl> wrote:


On 10 Jun 2019, at 12:04, Hans van der Meer <havdmeer@ziggo.nl> wrote:

This looks to me as an error in the LMTX distribution:

tex error       > tex error on line 6 in file /Users/hansm/TeX/context-lmtx/tex/texmf-context/tex/context/fonts/mkiv/type-imp-dejavu.mkiv: ! Missing } inserted

<inserted text> 
}
<to be read again> 
\aligntab 
l.6 fontclass\aligntab
                    \fontclass\cr

Because running under my old ConTeXtBeta does not aborts with the error.
system          > ConTeXt  ver: 2019.06.01 19:11 MKIV beta  fmt: 2019.6.4  int: english/english

I looked into that file but could not see what causes the error.

I did some more research and as a result now wonder what is happening.

The error occurred in this piece of code of mine:

\tabskip=1em\halign{%
\alignmark\hfil\aligntab\alignmark\hfil\cr
fontclass\aligntab\fontclass\cr
Regular\aligntab\truefontname{Regular}\cr
}

\aligntab and \alignmark were advertised as LuaTeX equivalents for & and # respectively.

Then I took the following example from Victor Eijkhout's book "TeX by Topic", page 197, last example.
That surely should work, was the idea.

\starttext
\halign{a#&b#&c#\cr 1&2\cr 1\cr}
\stoptext

However this fails! How can such a basic example in pure TeX fail? I wonder and am curious what is happening here.

This is LuaMetaTeX, Version 2.00.0 
tex error       > tex error on line 3 in file /Users/hansm/TeX/texmf/tex/context/user/type-loc.mkiv: ! Only one # is allowed per tab

l.3 \halign{a#&b#
               &c#\cr 1&2\cr 1\cr}

 1     \endinput
 2     
 3 >>  Op NTG ConTeXt nieuwsgroep, antwoord van Hans Hagen.
 4     
 5     On 1/3/2014 2:33 PM, H. van der Meer wrote:
 6     Has someone an idee what causes the unknown library message as in the
 7     log below? Is it harmful?
 8     
 9     fonts           > typescripts > unknown library 'loc'
10     
11     you can add a file type-loc.mkiv someplace in your local tree with
12     
13     % dummy file

There should be exactly one # between &'s, when an
\halign or \valign is being set up. In this case you had
more than one, so I'm ignoring all but the first.

mtx-context     | fatal error: return code: 256

and using \alignmark and \aligntab this results in:

\starttext
\halign{a\alignmark\aligntab b\alignmark\aligntab c\alignmark\cr 1\aligntab 2\cr 1\cr}
\stoptext

And I am most curious how my name could turn up in the error message produced!

tex error       > tex error on line 3 in file /Users/hansm/TeX/texmf/tex/context/user/type-loc.mkiv: ! Missing } inserted

<inserted text> 
}
<to be read again> 
\aligntab 
l.3 ...\alignmark\aligntab c\alignmark\cr 1\aligntab
                                                   2\cr 1\cr}

 1     \endinput
 2     
 3 >>  Op NTG ConTeXt nieuwsgroep, antwoord van Hans Hagen.
 4     
 5     On 1/3/2014 2:33 PM, H. van der Meer wrote:
 6     Has someone an idee what causes the unknown library message as in the
 7     log below? Is it harmful?
 8     
 9     fonts           > typescripts > unknown library 'loc'
10     
11     you can add a file type-loc.mkiv someplace in your local tree with
12     
13     % dummy file

I've put in what seems to be necessary to fix
the current column of the current alignment.
Try to go on, since this might almost work.

mtx-context     | fatal error: return code: 256




dr. Hans van der Meer


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