documentation for the new features in ltnews31

base/changes.txt

@@ -13,16 +13,18 @@ are not part of the distribution.
 	* fontdef.dtx (subsection{Defaults}): Set
 	\shapedefault explicitly to "n" not \updefault
 	\bfdefault set to to "b" not "bx" (but bx for CM fonts)
-	\updefault set to to "up" not "n"
+	\updefault set to to "up" not "n".
+	Part of extending the series and shape handling, see ltnews31.
 
 2019-12-17  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
 
 	* ltfssini.dtx (section{Supporting nested emphasis}):
 	Support nested \emph sequences a generalization \eminnershape.
 	See ltnews31 for details.
-	* ltfssini.dtx (section{Custom series settings for main document families}):
-	Provide custom series settings a la mweights
 
+	* ltfssini.dtx (section{Custom series settings for main document families}):
+	Provide custom series settings a la mweights package.
+	See ltnews31 for details.
 
 2019-12-17  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
 

base/doc/ltnews31.tex

@@ -232,19 +232,144 @@ \section{Improved load-times for \pkg{expl3}}
 
 
 
-\section{Extending the shape management with NFSS}
-
-\emph{write}
-
-
-
-\section{Extending the series management with NFSS}
-
-\emph{write}
-
+\section{Improvements to \LaTeX{}'s font selection mechanisms (NFSS)}
+
+
+\subsection{Extending the shape management of NFSS}
+
+Over time more and more fonts have become available for use with
+\LaTeX{}. Many such font families offer additional shapes, e.g., small
+caps italics (\texttt{scit}), small caps slanted (\texttt{scsl} or
+swash letters (\texttt{sw}). By using \cs{fontshape} those shapes can
+be explicitly selected and for the swash letter shapes there is also
+\cs{swshape} and \cs{textsw} available.
+
+In the original font selection implementation a request to new shape
+always a canceled the current one. With the 2020 release of \LaTeX{}
+this has changed and \cs{fontshape} can now be used to combine small
+capitals with italics, slanted or swash letters, either by explicitly
+asking for \texttt{scit}, etc., or by asking for italics when typesetting
+already in small caps and so forth.
+
+Using \cs{upshape} will still change italics or slanted back to an
+upright shape but will not any longer alter the small caps setting. To
+change small capitals back to upper/lower case you can now use
+\cs{ulcshape} (or \cs{textulc}) which in turn will not change the font
+with respect to italics, slanted or swash. Finally, if you want to
+reset the shape back to normal you can use \cs{normalshape} which is a
+shorthand for \cs{upshape}\cs{ulcshape}.
+
+The way how shapes combine with each other is not hardwired but is
+customizable and extensible if there is ever a need for it. The
+mappings are defined through \cs{DeclareFontShapeChangeRule} and the
+details for developers are documented in \texttt{source2e.pdf}.
+
+The ideas for this interface extension has been pioneered in
+\pkg{fontspec} by Will Roberson for Unicode engines and in
+\pkg{fontaxes} by Andreas Bühmann and Michael Ummels for \pdfTeX{} and
+used in many font support packages.
+
+
+
+\subsection{Extending the series management of NFSS}
+
+Many of the the newer font families also come provided with additional
+weights (thin, semi-bold, ultra-bold, etc.\@) or several running lengths
+such a condensed or extra-condensed. In some cases the number of
+different series values is really impressive, for example, Noto Sans
+offers 36 from ultra-light extra condensed to ultra-bold medium width.
+
+Already in its original design NFSS supported 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}) so more than enough even for a font family like Noto
+Sans. Unfortunately, some font support packages nevertheless invented
+their own names so in the last years you could find all kind of
+non-standard series names like \texttt{k}, \texttt{i}, \texttt{j} and
+others making it impossible to combine different fonts successfully
+using the standard NFSS mechanisms.
+
+Over the course of the last year a small number of individuals,
+notably, Bob Tennent, Michael Sharpe and Marc Penninga worked hard to
+bring this unsatisfying situation back under control and today we are
+happy to report and the internal font support files for more than a
+hundred font families are back to follow the standard NFSS conventions
+so that combing them is now again rather nice and easy (of course,
+there is still the task of choosing combinations that visually work
+well together, but from a technical perspective they can now easily
+matched).
+
+
+In the original font selection implementation a request to series
+always canceled the current one. This was reasonable because there
+were nearly no fonts available that offered anything other than a
+medium or a bold series. Now that this has changed and families such
+as Noto Sans are available, combing weight and width into a single
+attribute is no longer appropriate. With the 2020 release of \LaTeX{}
+the series management therefore changed to allow for independently
+setting the weight and the width attribute of the series.
+
+For most users this change will be largely transparent as \LaTeX{}
+offers only \cs{textbf} or \cs{bfseries} to select a bolder face (and
+\cs{textmd} and \cs{mdseries} to return to a medium series) but no
+high-level command for selecting a condensed face, etc. However, with
+the NFSS low-level interface, it is now possible to ask for, say,
+\verb=\fontseries{c}\selectfont= in a marginal note to get a condensed
+face and that would still allow  using \cs{textbf} inside. This then would
+select a bold condensed face and not a rather odd-looking
+bold-extended face in the middle of condensed type.
+
+The expectation is that this is largely used by class and package
+designers, but given that the low-level NFSS commands are usable on
+the document level and not really difficult to apply, there are
+probably also a number of users who will enjoy using the new
+possibilities that bring \LaTeX{} back into the front league when it
+comes to font usage.
+
+The way how different series values combine with each other is not
+hardwired but is again customizable and extensible. The mappings are
+defined through \cs{DeclareFontSeriesChangeRule} and the details for
+developers are documented in \texttt{source2e.pdf}.
+
+
+%\[ * \quad * \quad * \]
+
+\subsection{Font series defaults per document family}
+
+With additional weights and widths available in many font families it
+becomes more likely that somebody wants to match, say, a medium weight
+serif family with a semi-light sans serif family or that with one
+family one wants to use the bold-extend face when \cs{textbf} is used
+while with another it should be bold (not extended) or semibold, etc.
+
+In the past this kind of extension was made available with the
+\pkg{mweights} package by Bob Tennent which has been used in many font
+support packages.
+
+With the 2020 release of \LaTeX{} this feature is now available out
+of the box.  In addition we also offer a document-level interface to adjust the
+behavior high-level series commands \cs{textbf}, \cs{textmd} and their
+declaration forms \cs{bfseries} and \cs{mdseries} so that they can
+have different effects for the serif, sans serif and typewriter
+families used in a document.
+
+For example, specifying
+\begin{verbatim}
+  \DeclareFontSeriesDefault[rm]{bf}{sb}
+  \DeclareFontSeriesDefault[tt]{md}{lc}
+\end{verbatim}
+in the document preamble would result in \cs{textbf} producing
+semi-bold (\texttt{sb}) when typesetting in roman typeface and second
+declaration means that typewriter is by default (medium series) using
+a light-condensed face. The optional argument here can be either
+\texttt{rm}, \texttt{sf} or \texttt{tt} to indicate one of the three
+main font families in a document; if omitted you will change the
+overall document default instead.  In the first mandatory argument you
+specify either \texttt{md} or \texttt{bf} and the second mandatory
+argument then gives the desired series value in NFSS nomenclature.
 
 
-\section{Emphasis handling generalized}
+\subsection{Emphasis handling generalized}
 
 With previous releases of \LaTeX{} nested \cs{emph} commands
 automatically alternated between italics and upright.  This mechanism
@@ -258,7 +383,7 @@ \section{Emphasis handling generalized}
   \DeclareEmphSequence{\itshape,%
                \upshape\scshape,\itshape}
 \end{verbatim}
-uses italics for the first, small capitals for the second, and italic
+uses italics for the first, small capitals for the second, and italic
 small capitals for the third level (provided you use a font that
 supports these shapes).  If there are a more nesting levels than
 provided, \LaTeX{} uses the declarations stored in \cs{emreset} (by
@@ -279,6 +404,31 @@ \section{Emphasis handling generalized}
 
 
 
+\subsection{Providing font family substitutions}
+
+Given that \pdfTeX{} can only handle fonts with up to 256 glyphs a
+single font encoding can only support a few languages. The \texttt{T1}
+encoding, for example, does support many of the Latin based scripts,
+but if you want to write in Greek or Russian you need to switch
+encodings to \texttt{LGR} or \texttt{T2A}. Given that not every font
+family offers glyphs in such encodings, you may end up with some
+default family (e.g., Computer Modern) that doesn’t blend in well
+chosen document font.  For such cases NFSS now offers
+\cs{DeclareFontFamilySubstitution}, for example:
+\begin{verbatim}
+  \DeclareFontFamilySubstitution{LGR}
+       {Montserrat-LF}{IBMPlexSans-TLF}
+\end{verbatim}
+tells \LaTeX{} that if you are typesetting in the sans serif font
+\texttt{Montserrat-LF} and the Greek encoding \texttt{LGR} is asked
+for, then \LaTeX{} should use \texttt{IBMPlexSans-TLF} to fulfill the
+encoding request.
+
+The code is based on ideas from the \texttt{substitutefont}
+package by Günter Milde, but implemented differently.
+
+
+
 \section{Other changes to the \LaTeX{} kernel}
 
 \emph{added \texttt{alias} size function}

base/ltfssbas.dtx

@@ -1320,7 +1320,7 @@
 
 %  \begin{macro}{\DeclareFontFamilySubstitution}
 %    The idea for this macro is stolen from the \texttt{substitutefont}
-%    package, with some modifications and a new name.
+%    package by Günter Milde, with some modifications and a new name.
 %
 %    Its purpose is to provide characters in a special encoding tht
 %    are not available in the current font family to be taken from a