trunk/doc/ltnews22.tex

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  29 % Filename: ltnews22.tex
  30 %
  31 % This is issue 22 of LaTeX News.
  32
  33 \documentclass{ltnews}
  34 \usepackage[T1]{fontenc}
  35
  36 \usepackage{lmodern,url,hologo}
  37
  38 \publicationmonth{January}
  39 \publicationyear{2015}
  40
  41 \publicationissue{22}
  42
  43 \begin{document}
  44
  45 \maketitle
  46
  47 \section{New \LaTeXe\ bug-fix policy}
  48
  49 \subsection{Introduction}
  50
  51 For some years we have supplied bug fixes to the \LaTeXe\ kernel via the
  52 \textsf{fixltx2e} package. This
  53 kept the kernel stable, but at the expense of meaning that most users did not
  54 benefit from bug fixes, and that some compromises
  55 which were made to save space in the
  56 machines of the time are still affecting most users today.
  57
  58 In this release we have started a new update policy. All the fixes previously
  59 available via \textsf{fixltx2e} are now enabled \emph{by default} in the
  60 format, as are some further extensions for extended \TeX\ engines, \eTeX,
  61 \hologo{XeTeX} and \hologo{LuaTeX}. Compatibility and stability are still
  62 important considerations, and while most users will not notice these
  63 improvements, or will want to benefit from them, a new \textsf{latexrelease}
  64 package is provided that will revert all the changes and re-instate the
  65 definitions from earlier releases. The package can also be used with older
  66 releases to effectively \emph{update} the kernel to be equivalent to this 2015
  67 release.
  68
  69 A new document, \textsf{latexchanges}, is distributed with the release
  70 that documents all the changes to documented commands since the 2014
  71 \LaTeX\ release, and will be updated in future releases if further
  72 changes have been made.
  73
  74 \subsection{The \textsf{latexrelease} package}
  75
  76 As noted above a new package is available to manage differences between \LaTeX\
  77 releases. If you wish to revert all changes back to the definitions as they
  78 were in previous releases you may start your document requesting the \LaTeX{} release from May~2014:
  79 \begin{verbatim}
  80 \RequirePackage[2014/05/01]{latexrelease}
  81 \documentclass{article}
  82 \end{verbatim}
  83 Conversely if you start a large project now and want to protect yourself
  84 against possible future changes, you may start your document
  85 \begin{verbatim}
  86 \RequirePackage[2015/01/01]{latexrelease}
  87 \documentclass{article}
  88 \end{verbatim}
  89 Then the version of \textsf{latexrelease} distributed with any future \LaTeX\
  90 release will revert any changes made in that format, and revert to the
  91 definitions as they where at the beginning of 2015.
  92
  93 If you wish to share a document using the latest features with a
  94 user restricted to using an older
  95 format, you may use the form above and make the \textsf{latexrelease} package
  96 available on the older installation.  The package will then update the format
  97 definitions as needed to enable the older format to work as if dated on the date
  98 specified in the package option.
  99
 100 \subsection{The \cs{IncludeInRelease} command}
 101
 102 The mechanism used in the \textsf{latexrelease} package is available for use in
 103 package code. If in your \textsf{zzz} package you have
 104 \begin{verbatim}
 105 \RequirePackage{latexrelease}
 106 \IncludeInRelease{2015/06/01}
 107     {\zzz}{\zzz definition}
 108   \def\zzz......new code
 109 \EndIncludeInRelease
 110 \IncludeInRelease{0000/00/00}
 111   {\zzz}{\zzz definition}
 112   \def\zzz....original
 113 \EndIncludeInRelease
 114 \end{verbatim}
 115 then in a document using a format dated 2015/06/01 or later, the ``new code''
 116 will be used, and for documents being processed with an older format, the
 117 ``original'' code will be used. Note the format date here may be the original
 118 format date as shown at the start of every \LaTeX\ run, or a format date
 119 specified as a package option to the \textsf{latexrelease} package.
 120
 121 So if the document has
 122 \begin{verbatim}
 123 \RequirePackage[2014/05/01]{latexrelease}
 124 \documentclass{article}
 125 \usepackage{zzz}
 126 \end{verbatim}
 127 then it will use the \emph{original} definition of \verb|\zzz| even if
 128 processed with the current format, as the format acts as if dated 2014/05/01.
 129
 130
 131 \subsection{Limitations of the approach}
 132
 133 The new concept provides full backward and forward compatibility for
 134 the \LaTeX{} format, i.e., with the help of a current
 135 \textsf{latexrelease} package the kernel can emulate all released
 136 formats (starting with 2014/06/01\footnote{Patching an older format
 137   most likely works too, given that the changes in the past have been
 138   minimal, though this isn't guaranteed and hasn't been tested.}).
 139
 140
 141 However, this is not necessarily true for all packages.
 142  Only if a package makes use of the \cs{IncludeInRelease}
 143 functionality will it adjust to the
 144 requested \LaTeX{} release date. Initially this will only be true for
 145 a few selected packages and in general it may not even be advisable for packages
 146 that have their own well-established release cycles and methods.
 147
 148 Thus, to regenerate a document with 100\,\% compatible behavior
 149 it will still be necessary
 150 to archive it together with all its inputs, for example, by archiving
 151 the base distribution trees (and any modifications made). However, the
 152 fact that a document requests a specific \LaTeX{} release date should
 153 help identifying what release tree to use to achieve perfect accuracy.
 154
 155
 156 \section{Updates to the kernel}
 157
 158 \subsection{Updates incorporated from \textsf{fixltx2e}}
 159
 160 The detailed list of changes incorporated from \textsf{fixltx2e} is
 161 available in the new \textsf{latexchanges} document that is
 162 distributed with this release. The main changes are that $2$-column
 163 floats are kept in sequence with one column floats, corrections are
 164 made to the \verb|\mark| system to ensure correct page headings in
 165 $2$-column documents, several additional commands are made robust.
 166
 167 \subsection{\eTeX\ register allocation}
 168
 169 \LaTeX\ has traditionally used allocation routines inherited from plain \TeX\
 170 that allocated registers in the range $0$--$255$. Almost all distributions have
 171 for some years used \eTeX\ based formats (or \hologo{XeTeX} or \hologo{LuaTeX})
 172 which have $2^{15}$ registers of each type ($2^{16}$ in the case of
 173 \hologo{LuaTeX}). The \textsf{etex} package has been available to provided an
 174 allocation mechanism for these extended registers but now the format will by
 175 default allocate in a range suitable for the engine being used. The new
 176 allocation mechanism is different than the \textsf{etex} package mechanism, and
 177 supports \hologo{LuaTeX}'s full range and an allocation mechanism for \LaTeX\
 178 floats as described below.
 179
 180 On \eTeX\ based engines, an additional command, \verb|\newmarks| is available
 181 (as with the \textsf{etex} package) that allocates extended \eTeX\ marks, and
 182 similarly if \hologo{XeTeX} is detected a new command
 183 \verb|\newXeTeXintercharclass| is available, this is similar to the command
 184 previously defined in the \texttt{xelatex.ini} file used to build the
 185 \texttt{xelatex} format.
 186
 187 \subsection{Additional \LaTeX{} float storage}
 188
 189 \LaTeX's float placement algorithm needs to store floats (figures and tables)
 190 until it finds a suitable page to output them. It allocates $18$ registers for
 191 this storage, but this can often be insufficient.
 192  The contributed \textsf{morefloats} package has
 193 been available to extend this list; however, it also only allocates from the
 194 standard range $0$--$255$ so cannot take advantage of the extended registers.
 195 The new allocation mechanism in this release incorporates a new command
 196 \verb|\extrafloats|. If you get the error:
 197 \mbox{\texttt{Too many unprocessed floats.}}
 198 then you can add (say) \verb|\extrafloats{500}| to the document preamble to
 199 make many more boxes available to hold floats.
 200
 201
 202 \subsection{Built-in support for Unicode engines}
 203
 204 The kernel sources now detect the engine being used and adjust definitions
 205 accordingly, this reduces the need for the ``\texttt{.ini}'' files used to make
 206 the formats to patch definitions defined in \texttt{latex.ltx}.
 207
 208 As noted above the format now includes extended allocation routines.
 209
 210 The distribution includes a file \textsf{unicode-letters.def} derived from the
 211 Unicode Consortium's Unicode Character Data files that details the upper and
 212 lower case transformation data for the full Unicode range. This is used to set
 213 the \verb|lccode| and \verb|uccode| values if a Unicode engine is being used,
 214 rather than the values derived from the T1 font encoding which are used with
 215 8-bit engines.
 216
 217 Finally \verb|\typein| is modified if \hologo{LuaTeX} is detected
 218 such that it works with this engine.
 219
 220 \section{l3build}
 221
 222 This release has been tested and built using a new build system implemented in
 223 \textsf{Lua}, intended to be run on the \textsf{texlua} interpreter distributed
 224 with modern \TeX\ distributions. It is already separately available
 225 from CTAN. This replaces earlier build systems (based at various times on
 226 \textsf{make}, \textsf{cons}, and Windows \textsf{bat} files). It allows the
 227 sources to be tested and packaged on a range of platforms (within the team,
 228 OS X, Windows, Linux and Cygwin platforms are used). It also allows the
 229 format to be tested on \hologo{XeTeX} and \hologo{LuaTeX} as well as the
 230 standard \hologo{pdfTeX}/\eTeX\ engines.
 231
 232 \section{Hyperlinked documentation and TDS zip files}
 233
 234 As well as updating the build system, the team have looked again at exactly
 235 what gets released to \textsc{ctan}. Taking inspiration from Heiko Oberdiek's
 236 \textsf{latex-tds} bundle, the PDF documentation provided now includes
 237 hyperlinks where appropriate. This has been done without modifying the sources
 238 such that users without \textsf{hyperref} available can still typeset the
 239 documentation using only the core distribution. At the same time, the release
 240 now includes ready-to-install TDS-style zip files. This will be of principal
 241 interest to \TeX\ system maintainers, but end users with older machines who
 242 wish to manually update \LaTeX\ will also benefit.
 243
 244 \end{document}