Series changes (a version of #1396)

base/changes.txt

@@ -6,6 +6,13 @@ to completeness or accuracy and it contains some references to files that are
 not part of the distribution.
 ================================================================================
 
+2024-12-13  Maurice Hansen & Frank Mittelbach
+
+        * ltfssaxes.dtx
+        Add numerous \DeclareFontSeriesChangeRule entries to support the full
+        range of weights (from 'ul' to 'ub') and widths (from 'uc' to 'ux').
+        Minor modifications to the existing entries. (gh/1583)
+
 2024-12-11  Frank Mittelbach  <[email protected]>
 
 	* ltfssaxes.dtx (subsection{Mapping rules for shape combinations}):

base/doc/ltnews41.tex

@@ -270,6 +270,55 @@ \subsection{Logging text command and symbol declarations}
 %
 \githubissue{1242}
 
+\subsection{Supporting the \texttt{ssc} and \texttt{sw} shapes}
+
+The \texttt{ssc} shape (spaced small capitals) is supported in
+\LaTeX{} through the commands \cs{sscshape} and \cs{textssc}. However,
+until this release there where no font shape change rules defined for
+this admittely seldom available shape, so that
+\begin{verbatim}
+  \sscshape\itshape
+\end{verbatim}
+changed unconditionally to \texttt{it} (italics) rather than to
+\texttt{sscit} (spaced small italic capitals).  Thanks to Michael
+Ummels, the missing declarations have now been added so that shape
+changes in font families that support spaced small capitals work
+properly.
+
+At the same time we took the opportunity to improve the fallbacks for
+the \texttt{sw} (swash) shapes, which are accessible through the
+commands \cs{swshape} or \cs{textsw}. If an \texttt{sw} combination is
+not available, the rules now try to replace \texttt{sw} with
+\texttt{it} rather than falling back to \texttt{n}.
+%
+\githubissue{1581}
+
+\subsection{Improvement of the NFSS font series management}
+
+\LaTeX's font selection mechanism (NFSS) supports 9~weight levels,
+from ultra-light~(\texttt{ul}) to ultra-bold~(\texttt{ub}), and also
+9~width levels, from ultra-condensed~(\texttt{uc}) to
+ultra-expanded~(\texttt{ux}). With the February~2020 release, this
+mechanism was extended so that requests to set the weight or the width
+attributes of the series are combined in a sensible
+way~\cite{41:ltnews31}: E.g., if you typeset a paragraph in a
+condensed face using \verb+\fontseries{c}\selectfont+ and then use
+\cs{textbf} inside the paragraph, a bold condensed face is
+selected. The combination of the series values is done by consulting a
+simple lookup table whose entries are defined with
+\cs{DeclareFontSeriesChangeRule}.
+
+Until now, this lookup table was missing some entries, especially with
+regard to rarely used width values. In such cases, the series values
+were not combined as expected. This has been fixed (thanks to Maurice
+Hansen) by adding numerous \cs{DeclareFontSeriesChangeRule} entries so
+that the full range of weights (from \texttt{ul} to \texttt{ub}) and
+widths (from \texttt{uc} to \texttt{ux}) is now supported when
+combining font series values.
+%
+\githubissue{1396}
+
+
 \subsection{Supporting the \texttt{ssc} and \texttt{sw} shapes}
 
 The \texttt{ssc} shape (spaced small capitals) is supported in
@@ -354,6 +403,10 @@ \subsection{\pkg{multicol}:\ Full support for extended marks}
   \emph{\LaTeXe{} news 1--41}. June, 2025.
   \url{https://latex-project.org/news/latex2e-news/ltnews.pdf}
 
+\bibitem{41:ltnews31} \LaTeX{} Project Team.
+  \emph{\LaTeXe{} news 31}. February 2020.
+  \url{https://latex-project.org/news/latex2e-news/ltnews31.pdf}
+
 \bibitem{41:ltnews34} \LaTeX{} Project Team.
   \emph{\LaTeXe{} news 34}. November 2021.
   \url{https://latex-project.org/news/latex2e-news/ltnews34.pdf}