trunk/doc/ltnews26.tex

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  29 % Filename: ltnews26.tex
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  31 % This is issue 26 of LaTeX News.
  32
  33 \documentclass{ltnews}
  34 \usepackage[T1]{fontenc}
  35
  36 \usepackage{lmodern,url,hologo}
  37
  38
  39 \publicationmonth{December}
  40 \publicationyear{2016}
  41
  42 \publicationissue{26}
  43
  44 \begin{document}
  45
  46 \maketitle
  47 \tableofcontents
  48
  49 \rightskip=0pt plus 3em
  50 \section{\eTeX{}}
  51
  52 In \LaTeX{} News~16 (December 2003) the team announced
  53 \begin{quotation}
  54 We expect that within the next two years, releases of \LaTeX{} will
  55 change modestly in order to run best under an extended \TeX{} engine
  56 that contains the \eTeX{} primitives, e.g., \eTeX{} or pdf\TeX{}.
  57 \end{quotation}
  58 and also said
  59 \begin{quotation}
  60 Although the current release does not \emph{require} \eTeX{} features, we
  61 certainly recommend using an extended \TeX{}, especially if you need to debug
  62 macros.
  63 \end{quotation}
  64
  65 For many years the team have worked on the basis that users will have \eTeX{}
  66 available but had not revisited the above statements formally. As of the
  67 January 2017 release of \LaTeXe{}, \eTeX{} is \emph{required} to build the
  68 format, and attempting to build a format without the extensions will fail.
  69
  70 Practically, modern \TeX{} distributions provide the extensions in all engines
  71 other than the ``pure'' Knuth \texttt{tex}, and indeed parts of the
  72 format-building process already require \eTeX{}, most notably some of the UTF-8
  73 hyphenation patterns. As such, there should be no noticeable affect on users of
  74 this change.
  75
  76 The team expect to make wider use of \eTeX{} within the kernel in future;
  77 details will be announced where they impact on end users in a visible way.
  78
  79 \section{Default Encodings in \hologo{XeLaTeX} and \hologo{LuaLaTeX}}
  80 The default encoding in \LaTeX\ has always been the original
  81 127-character encoding OT1.  For Unicode based \TeX\ engines, this
  82 is not really suitable, and is especially problematic with
  83 \hologo{XeLaTeX} as in the major distributions this is built with
  84 Unicode base hyphenation patterns in the format.  In practice this has
  85 not been a major problem as documents use the contributed
  86 \textsf{fontspec} package in order to switch to a
  87 Unicode encoded font.
  88
  89 In this release we are adding TU as a new supported
  90 encoding in addition to the previously supported encodings such as OT1
  91 and T1. This denotes a Unicode based font encoding. It is essentially
  92 the same as the TU encoding that has been on trial with the
  93 experimental \texttt{tuenc} option to \textsf{fontspec} for the past
  94 year.
  95
  96 The \hologo{XeLaTeX} and \hologo{LuaLaTeX} formats will now default
  97 to \texttt{TU} encoding and \texttt{lmr} (Latin Modern) family. In the
  98 case of \hologo{LuaLaTeX} the contributed \textsf{luaotfload} Lua
  99 module will be loaded at the start of each run to enable the loading
 100 of OpenType fonts.
 101
 102 The \textsf{fontspec} package is being adjusted in a companion release
 103 to recognise the new encoding default arrangements.
 104
 105 Note that in practice no font supports the full Unicode range, and so
 106 TU encoded fonts, unlike fonts specified for T1, may be expected to be
 107 incomplete in various ways. In the current release the file
 108 \texttt{tuenc.def} that implements the TU encoding-specific commands
 109 has made some basic assumptions for (for example) default handling of
 110 accent commands, and the set of command names is derived from the
 111 command names used for the UTF-8 support in the inputenc package,
 112 restricted roughly to the character ranges classically provided by
 113 the T1 and TS1 encodings, but is part of a longer term plan seen over
 114 recent releases to increase support for Unicode based \TeX\ engines into
 115 the core \LaTeX\ support.
 116
 117
 118
 119 If for any reason you need to process a document with the previous
 120 default OT1 encoding, you may switch encoding in the usual ways, for
 121 example
 122 \begin{verbatim}
 123 \usepackage[OT1]{fontenc}
 124 \end{verbatim}
 125 or you may roll back all the changes for this release by starting the
 126 document with
 127 \begin{verbatim}
 128 \RequirePackage[2016/03/31]{latexrelease}
 129 \end{verbatim}
 130
 131 \section{The \textsf{latexbug} package}
 132
 133 As explained in more detail
 134 \href{https://www.latex-project.org/bugs/}{at the \LaTeX\ Project
 135   website},
 136 A new package, \textsf{latexbug}, has been produced to help produce
 137 test files to accompany bug reports on the core \LaTeX\ distribution.
 138 This is being published separately to CTAN at the same time as this
 139 release. By using the \textsf{latexbug} package you can easily check
 140 that the packages involved in the test are all part of the core
 141 release. The \LaTeX\ project can not handle bug reports on contributed
 142 packages, which should be directed to the package maintainer as given
 143 in the package documentation.
 144
 145 \section{Updates to \textsf{amsmath}}
 146 The \textsf{amsmath} package has two updates at this release.
 147 \begin{itemize}
 148 \item The spacing to the left of the \texttt{aligned} and
 149   \texttt{gathered} environments has been fixed, the spurious thin
 150   space is no longer added by default. Package options control this
 151   to revert to the original behaviour where required, see the
 152   \textsf{amsldoc} guide for further details.
 153 \item The large delimiters around generalised fractions (for example
 154   in the \verb|\binom| construct) did not work in previous releases if
 155   using Lua\TeX or Xe\TeX\ with OpenType math fonts. This is releated
 156   to the lack of specific metrcs for this use in the OpenType Math
 157   table. In principle Lua\TeX\ has two additional named metrics
 158   to control the delimiters but these are not initialised by default,
 159   and in Xe\TeX\ it does not seem possible to make them work at all.
 160   So for Unicode \TeX\ systems, a new implementation of
 161   \verb|\genfrac| is used at this release that uses \verb|\left\right|
 162   internally but parameterised to give spacing as close to the
 163   original as possible. The implementation in (pdf)\TeX\ is
 164   unaffected.
 165 \end{itemize}
 166
 167 \section{An addendum to the release changes in 2015}
 168
 169 In 2015 we announced the introduction of the roll-back\slash
 170 roll-forward concept to manage bug fixes and additions to core
 171 \LaTeX{} in a manageable way for the user base. We also announced back
 172 then that we now incorporate all fixes from \textsf{fixltx2e} into the
 173 kernel (as the old mechanism produced problems instead of improving
 174 the situation). Refer to
 175 \href{https://www.latex-project.org/news/latex2e-news/ltnews22.pdf}{\texttt{ltnews22.pdf}}
 176 for details.
 177
 178 One of the fixes from \textsf{fixltx2e} was for a glaring bug in
 179 \cs{addvspace} that was originally detected in the mid-nineties and
 180 back then added to the \textsf{fixltx2e} support package. In certain
 181 situations \cs{addvspace} would result in a page/column break below
 182 the baseline of the last line. As a result documents using
 183 \cs{flushbottom} would show a clear misalignment (even more prominent
 184 when typesetting in two-column mode).
 185
 186 Starting with release 2015/01/01 this is now finally corrected already
 187 in the kernel and not only in \textsf{fixltx2e}. In nearly all
 188 circumstances this will either not make any difference to existing
 189 documents or if it does locally impove the visual appearence of that
 190 document. It is, however, by the nature of the change also possible
 191 that there are changes to the page breaks due to the different break
 192 positions introduced by the fix.
 193
 194 Thus, for documents that have been written before 2015 and that should
 195 be preserved unchanged at all costs you may have to add
 196 \begin{verbatim}
 197 \RequirePackage[2014/01/01]{latexrelease}
 198 \end{verbatim}
 199 at the top of the document, to roll back the format to a date before
 200 the policy change.
 201
 202 \end{document}