[latex3-commits] [git/LaTeX3-latex3-latex2e] master: @ifundefined (2355226)

[David Carlisle]

Repository : https://github.com/latex3/latex2e
On branch  : master
Link       : https://github.com/latex3/latex2e/commit/2355226edf2ab481ce657bdf953c997512d3ebd1

>---------------------------------------------------------------

commit 2355226edf2ab481ce657bdf953c997512d3ebd1
Author: David Carlisle <d.p.carlisle at gmail.com>
Date:   Fri Mar 30 21:33:31 2018 +0100

    @ifundefined


>---------------------------------------------------------------

2355226edf2ab481ce657bdf953c997512d3ebd1
 doc/ltnews28.tex |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/doc/ltnews28.tex b/doc/ltnews28.tex
index 34fac81..06ab253 100644
--- a/doc/ltnews28.tex
+++ b/doc/ltnews28.tex
@@ -254,13 +254,22 @@ counter (and recursively all other heading counters). However, what
 was until now missing was a way to undo such a link between counters
 or to link two counters after they have been defined.
 
-This can be now down with \cs{counterwithin} and \cs{counterwithout},
+This can be now be done with \cs{counterwithin} and \cs{counterwithout},
 respectively. In the past one had to load the \pkg{chngcntr} package
 for this. For the programming level we also added
-\cs{@removefromreset} as the counterpart o the already existing
+\cs{@removefromreset} as the counterpart of the already existing
 \cs{@addtoreset} command. Up to now this was offered by the
 \pkg{remreset} package.
 
+\section{Testing for undefined commands}
+\LaTeX\ packages often use a test \verb|\@ifundefined| to test if a command
+is defined. Unfortunately this had the side effect of \emph{defining}
+the command to \verb|\relax| in the case that it had no definition.
+ The new release uses a modified definition
+(using extra testing possibilities available in \hologo{eTeX}. The new definition
+is more natural, however code that was relying on the side effect of the
+command being tested being defined if it was previously undefined may have to add
+\verb|\let\|\meta{command}\verb|\relax|.
 
 
 \section{Changes to packages in the tools category}