Am 18.04.2013 um 14:55 schrieb "Meer, H. van der" <H.vanderMeer@uva.nl>:

> There seems something very much amiss with \halign in later ConTeXt versions.
> 
> This typesets fine in PlainTeX and is an example taken from a textbook.
> 
>   \tabskip=1em\halign{%
>   \hfil\it#\hfil&\hfil#\hfil&#&\hfil#\crA&B&C&D\cr}
> 
> Also in contextversion 2012.05.30 (from a TeXlive distribution).
> 
> But it fails at least in ConTeXt  ver: 2013.03.20 10:34 MKIV
> and in ConTeXt  ver: 2013.04.16 12:08 MKIV beta
> with the following error
> 
> ! Only one # is allowed per tab.
> system          > tex > error on line 5 in file fixedwidth.tex: Only one # is allowed per tab ...
> 
>  1     \starttext
>  2     contextversion=\contextversion\par
>  3     \tabskip=1em
>  4     \halign{%
>  5 >>  \hfil\it#\hfil&\hfil#\hfil&#&\hfil#\cr
>  6     A&B&C&D\cr}
>  7     \stoptext
> l.5 \hfil\it#\hfil&\hfil#
>                        \hfil&#&\hfil#\cr
> 
> Why? How primitive it may be, I would like to use \halign now and then.

The error message is misleading because the problem is & and not #.

One of the changes for MkIV was to make _, ^ and & normal characters
in the document (the first two still works for math). For code writing this
doesn’t matter because & has it’s normal meaning when you use
\unprotect … \protect but it can’t be used in the document.

Wolfgang