Detail interaction of trailing optional args. and \inputlineno

latex3 · May 19, 2023 · 9cce659 · 9cce659
1 parent 1a3121a
commit 9cce659
Show file tree

Hide file tree

Showing 2 changed files with 12 additions and 0 deletions.
diff --git a/base/changes.txt b/base/changes.txt
@@ -5,6 +5,12 @@ It is provided for convenience only.  It therefore makes no claims to
 completeness or accuracy and it contains some references to files that
 are not part of the distribution.
 ================================================================================
+2023-05-97  Joseph Wright  <Joseph.Wright@latex-project.org>
+
+	* usrguide.tex (section Creating document commands and environments)
+	  Add details of result of trailing optional arguments on
+	  \inputlineno
+
 2023-05-12  Ulrike Fischer <Ulrike.Fischer@latex-project.org>
 
 	* ltxref.dtx

diff --git a/base/doc/usrguide.tex b/base/doc/usrguide.tex
@@ -340,6 +340,12 @@ \subsection{Spacing and optional arguments}
 \NewDocumentCommand\\{!s !o}{ ... }
 \end{verbatim}
 
+Also notable when using optional arguments in the last position is that \TeX{}
+will necessarily look ahead for the argument opening token. This means that
+the value of |\inputlineno| will be `out by one' if such a trailing optional
+argument is \emph{not} present and the command ends a line; it will be one
+greater than the line number containing the last mandatory argument.
+
 \subsection{`Embellishments'}
 \label{sec:cmd:embellishment}