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Sender: Mailing list for the LaTeX3 project <[log in to unmask]>
Date: Tue, 5 Apr 2016 10:02:11 +0100
Reply-To: Mailing list for the LaTeX3 project <[log in to unmask]>
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From: David Carlisle <[log in to unmask]>
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On 05/04/2016 09:42, Joseph Wright wrote:
> I wonder about the fact that e-TeX v1 -> v2 included adding \halign
> cells to places where \protected is 'active': presumably there was a
> good reason for this though it may (since Peter B.'s death) be hard to
> pin this down.

The driving force there were the usual problems of \if... tests doing
the wrong thing at start of array cells.

For \ifmmode that's usually avoidable by doing \relax\ifmmode but harder
(and caused us a lot of anguish at the time) is inputenc/fontenc style
tests: you want, if possible, any tests to be expandable so you don't
break kerns around accented letters, but if they are expandable and at
the start of a table cell typically they expand to the wrong thing.
Making the tests in a \protected macro would avoid that problem.....



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