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 \publicationmonth{January}
  39 \publicationyear{2017}
  40
  41 \publicationissue{26}
  42
  43 \begin{document}
  44
  45 \maketitle
  46 \tableofcontents
  47
  48 \setlength\rightskip{0pt plus 3em}
  49 \section{\eTeX{}}
  50
  51 In \LaTeX{} News~16 (December 2003) the team announced
  52 \begin{quotation}
  53 We expect that within the next two years, releases of \LaTeX{} will
  54 change modestly in order to run best under an extended \TeX{} engine
  55 that contains the \eTeX{} primitives, e.g., \eTeX{} or pdf\TeX{}.
  56 \end{quotation}
  57 and also said
  58 \begin{quotation}
  59 Although the current release does not \emph{require} \eTeX{} features, we
  60 certainly recommend using an extended \TeX{}, especially if you need to debug
  61 macros.
  62 \end{quotation}
  63
  64 For many years the team have worked on the basis that users will have \eTeX{}
  65 available but had not revisited the above statements formally. As of the
  66 January 2017 release of \LaTeXe{}, \eTeX{} is \emph{required} to build the
  67 format, and attempting to build a format without the extensions will fail.
  68
  69 Practically, modern \TeX{} distributions provide the extensions in all engines
  70 other than the ``pure'' Knuth \texttt{tex}, and indeed parts of the
  71 format-building process already require \eTeX{}, most notably some of the UTF-8
  72 hyphenation patterns. As such, there should be no noticeable effect on users of
  73 this change.
  74
  75 The team expect to make wider use of \eTeX{} within the kernel in future;
  76 details will be announced where they impact on end users in a visible way.
  77
  78 \section{Default Encodings in \hologo{XeLaTeX} and \hologo{LuaLaTeX}}
  79 The default encoding in \LaTeX\ has always been the original
  80 128-character encoding \texttt{OT1}.  For Unicode based \TeX\ engines, this
  81 is not really suitable, and is especially problematic with
  82 \hologo{XeLaTeX} as in the major distributions this is built with
  83 Unicode based hyphenation patterns in the format.  In practice this has
  84 not been a major problem as documents use the contributed
  85 \textsf{fontspec} package in order to switch to a
  86 Unicode encoded font.
  87
  88 In this release we are adding \texttt{TU} as a new supported
  89 encoding in addition to the previously supported encodings such as \texttt{OT1}
  90 and \texttt{T1}. This denotes a Unicode based font encoding. It is essentially
  91 the same as the \texttt{TU} encoding that has been on trial with the
  92 experimental \texttt{tuenc} option to \textsf{fontspec} for the past
  93 year.
  94
  95 The \hologo{XeLaTeX} and \hologo{LuaLaTeX} formats will now default
  96 to \texttt{TU} encoding and \texttt{lmr} (Latin Modern) family. In the
  97 case of \hologo{LuaLaTeX} the contributed \textsf{luaotfload} Lua
  98 module will be loaded at the start of each run to enable the loading
  99 of OpenType fonts.
 100
 101 The \textsf{fontspec} package is being adjusted in a companion release
 102 to recognise the new encoding default arrangements.
 103
 104 Note that in practice no font supports the full Unicode range, and so
 105 \texttt{TU} encoded fonts, unlike fonts specified for \texttt{T1}, may be
 106 expected to be incomplete in various ways. In the current release the file
 107 \texttt{tuenc.def} that implements the \texttt{TU} encoding-specific commands
 108 has made some basic assumptions for (for example) default handling of
 109 accent commands, and the set of command names is derived from the
 110 command names used for the UTF-8 support in the \textsf{inputenc} package,
 111 restricted roughly to the character ranges classically provided by
 112 the \texttt{T1} and \texttt{TS1} encodings, but is part of a longer term plan
 113 seen over recent releases to increase support for Unicode based \TeX\ engines
 114 into the core \LaTeX\ support.
 115
 116
 117
 118 If for any reason you need to process a document with the previous
 119 default \texttt{OT1} encoding, you may switch encoding in the usual ways, for
 120 example
 121 \begin{verbatim}
 122 \usepackage[OT1]{fontenc}
 123 \end{verbatim}
 124 or you may roll back all the changes for this release by starting the
 125 document with
 126 \begin{verbatim}
 127 \RequirePackage[2016/12/31]{latexrelease}
 128 \end{verbatim}
 129
 130 \section{\cs{showhyphens} in \hologo{XeLaTeX}}
 131 Due to the way \hologo{XeLaTeX} interfaces to font libraries, the
 132 standard definition of \cs{showhyphens} does not work.  A variant
 133 definition has been available in the contributed \textsf{xltxtra}
 134 package, however a (slightly different) definition for \cs{showhyphens}
 135 is now included in \hologo{XeLaTeX} by default. As usual
 136 this change will be undone if an earlier
 137 release is specified using the \textsf{latexrelease} package.
 138
 139 \section{The \textsf{fixltx2e} Package}
 140 As described in \LaTeX{} News~22, the \textsf{fixltx2e} package has become
 141 obsolete with the new update policy. Since 2015 it has just made a
 142 warning and exited.  In this release we have re-introduced all
 143 the code from the original fixes in the 2014 \LaTeX\ but guarded by
 144 \verb|\IncludeInRelease{2015/01/01}|.
 145 So for current releases \textsf{fixltx2e} still just makes a warning
 146 but for old releases, whether that is an old format, or a format with
 147 the version date reset via  the \textsf{latexrelease} package, the
 148 fixes in the original \textsf{fixltx2e} will be applied.
 149
 150 This improves the ability to run old documents in a way compatible
 151 with contemporary formats. If you have a 2014 document that used
 152 \verb|\usepackage{fixltx2e}| and you add
 153 \verb|\RequirePackage[2014/01/01]{latexrelease}| and process it with the
 154 current format then \textsf{latexrelease} will undo most changes made
 155 since 2014, but now when the document includes \textsf{fixltx2e} it
 156 will act like a 2014 version of the package and apply the code fixes,
 157 not just give a warning that the package is obsolete.
 158
 159 \section{The \textsf{latexbug} package}
 160
 161 As explained in more detail
 162 at the \LaTeX\ Project
 163   website\footnote{\url{https://www.latex-project.org/bugs/}}
 164 a new package, \textsf{latexbug}, has been produced to help produce
 165 test files to accompany bug reports on the core \LaTeX\ distribution.
 166 This is being published separately to CTAN at the same time as this
 167 release. By using the \textsf{latexbug} package you can easily check
 168 that the packages involved in the test are all part of the core
 169 release. The \LaTeX\ project can not handle bug reports on contributed
 170 packages, which should be directed to the package maintainer as given
 171 in the package documentation.
 172
 173 \section{Updates to \textsf{amsmath}}
 174 The \textsf{amsmath} package has two updates at this release.
 175 \begin{itemize}
 176 \item The spacing to the left of the \texttt{aligned} and
 177   \texttt{gathered} environments has been fixed: the spurious thin
 178   space is no longer added by default. Package options control this
 179   to revert to the original behaviour where required; see the
 180   \textsf{amsldoc} guide for further details.
 181 \item The large delimiters around generalised fractions (for example
 182   in the \cs{binom} construct) did not work in previous releases if
 183   using \hologo{LuaTeX} or \hologo{XeTeX} with OpenType math fonts. This is
 184   related to the lack of specific metrics for this use in the OpenType Math
 185   table. In principle \hologo{LuaTeX} has two additional named metrics
 186   to control the delimiters but these are not initialised by default,
 187   and in \hologo{XeTeX} it does not seem possible to make them work at all.
 188   So for Unicode \TeX\ systems, a new implementation of
 189   \cs{genfrac} is used at this release that uses \verb|\left\right|
 190   internally but parameterised to give spacing as close to the
 191   original as possible. The implementation in (pdf)\TeX\ is
 192   unaffected.
 193 \end{itemize}
 194
 195 \section{Updates to \textsf{tools}}
 196 The \textsf{array} package has been updated to fix a longstanding but
 197 previously unreported issue with unwanted interactions between tables
 198 in the page head or foot and the body of the page, as reported in
 199 \href{http://www.latex-project.org/cgi-bin/ltxbugs2html?pr=tools/4488}{PR
 200   tools/4488}.
 201 There is also an update to the \hologo{LuaTeX} support in \textsf{bm}.
 202
 203 \section{An addendum to the release changes in 2015}
 204
 205 In 2015 we announced the introduction of the roll-back\slash
 206 roll-forward concept to manage bug fixes and additions to core
 207 \LaTeX{} in a manageable way. We also announced at that time
 208 that we now incorporate all fixes from \textsf{fixltx2e} into the
 209 kernel (as the old mechanism produced problems instead of improving
 210 the situation). Refer to
 211 \href{https://www.latex-project.org/news/latex2e-news/ltnews22.pdf}{\texttt{ltnews22.pdf}}
 212 for details.
 213
 214 One of the fixes from \textsf{fixltx2e} was for a glaring bug in
 215 \cs{addvspace} that was originally detected in the mid-nineties and
 216 back then added to the \textsf{fixltx2e} support package. In certain
 217 situations \cs{addvspace} would result in a page/column break below
 218 the baseline of the last line. As a result documents using
 219 \cs{flushbottom} would show a clear misalignment (even more prominent
 220 when typesetting in two-column mode).
 221
 222 Starting with release 2015/01/01 this is now finally corrected already
 223 in the kernel and not only in \textsf{fixltx2e}.  In nearly all
 224 circumstances this will either make no difference to existing
 225 documents, or it will locally improve the visual appearence of that
 226 document without changing anything on other pages.  However, by the
 227 nature of the change it is also possible that there are further
 228 non-local changes to the page breaks due to the different break
 229 positions introduced by the fix.
 230
 231 Thus, for documents that have been written before 2015 and that should
 232 be preserved unchanged at all costs you may have to add
 233 \begin{verbatim}
 234 \RequirePackage[2014/01/01]{latexrelease}
 235 \end{verbatim}
 236 at the top of the document, to roll back the format to a date before
 237 the policy change.
 238
 239 \end{document}