Updated the draft for post-proceedings.

[luatex-ja/luatexja.git] / doc / ajt-devel-ltja.tex

%#!lualatex ajt-devel-ltja
\documentclass{ajt}

%%% Packages used in this paper
%%% LuaTeX-ja

\usepackage{luatexja}
\DeclareFontShape{JY3}{mc}{m}{n}{<-> s*[0.92489] file:ipam.ttf:jfm=ujis}{}
\DeclareFontShape{JY3}{gt}{m}{n}{<-> s*[0.92489] file:ipag.ttf:jfm=ujis}{}
% quick hack: monospaced Japanese font by \ttfamily
\DeclareKanjiFamily{JY3}{\ttdefault}{}{}
\DeclareFontShape{JY3}{\ttdefault}{m}{n}{<-> s*[0.92489] file:ipag.ttf:jfm=mono}{}

%%% for LTXexample environment
\usepackage{showexpl,lltjlisting}
\lstset{basicstyle=\ttfamily\small, width=0.3\textwidth, basewidth=.5em}

\usepackage{mflogo,booktabs}
\definecolor{gray10}{gray}{0.9}

%%% Verbatim environment
\usepackage{fancyvrb}
\CustomVerbatimEnvironment{code}{Verbatim}%
{numbers=left,xleftmargin=1.5em,baselinestretch=1.069,fontsize=\small}
\CustomVerbatimEnvironment{codewithoutnum}{Verbatim}%
{xleftmargin=1.5em,baselinestretch=1.069,fontsize=\small}
\CustomVerbatimEnvironment{codewithoutnumsmall}{Verbatim}%
{xleftmargin=1.5em,baselinestretch=1.0,fontsize=\footnotesize}
\DefineShortVerb{\|}

%%% Mandatory article metadata %%%
\title{Development of the \LuaTeX-ja package}
\author{Hironori Kitagawa {\normalsize 北川 弘典}}
\address{The \LuaTeX-ja project team}
\email{h\_kitagawa2001@yahoo.co.jp}

\keywords{\TeX, p\TeX, \LuaTeX, \LuaTeX-ja, Japanese}
\abstract{%
The \LuaTeX-ja package is a macro package for typesetting Japanese
documents under \LuaTeX.  This packages has more flexibility of
typesetting than p\TeX, and corrected some unwanted features of p\TeX.
In this paper, we describe specifications, the current status and some
internal processing methods of \LuaTeX-ja.
}

\newcommand{\parname}[1]{\textsf{#1}}
\newcommand{\jstrut}{\vrule width0pt height\cht depth\cdp}
\newcommand{\imagfm}[1]{\ifvmode\leavevmode\fi%
  \hbox{\fboxsep=0pt\fbox{\setbox0=\hbox{#1}\copy0\kern-\wd0
  \smash{\vrule width \wd0 height 0.4pt depth0.4pt}}}}
\begin{document}

%%% Do not forget to start with \maketitle!
\maketitle

\section{Introduction}
\subsection{History}
To typeset Japanese documents with \TeX, ASCII p\TeX~\cite{ptex} has
been widely used in Japan.  There are other methods---for example, using Omega
and OTP~\cite{omega}, or with the CJK package---to do so, however,
these alternative methods did not become a majority. On the one hand,
p\TeX\ enables us to produce high-quality documents. 

On the other hand, p\TeX\ is left behind from the extensions of \TeX\
such as \eTeX\ and \pdfTeX, and the diffusion of UTF-8 encoding.  In
recent years, the situation become better, because of developments
of |ptexenc|~\cite{ptexenc} by Nobuyuki Tsuchimura (\hbox{土村展之}),
$\varepsilon$-p\TeX~\cite{eptex} by the author,~and up\TeX~\cite{uptex}
by Takuji Tanaka (田中琢爾). However, continuing this approach, namely, to develop
an engine extension localized for Japanese, is not wise. This approach
needs lots of work for \emph{each} engine, and \LuaTeX\ has an ability
to hook \TeX's internal process by using Lua callbacks.


There were several experimental attempts to typeset
Japanese documents with \LuaTeX\ before. Here we cite three examples:
\begin{itemize}
\item |luaums.sty|~\cite{luaums} developed by the author. This
      experimental package is for creating a certain Japanese-based presentation
      with \LuaTeX.
\item the \emph{luajalayout} package~\cite{luajalayout}, formerly known as the
      \emph{jafontspec} package, by Kazuki Maeda (前田一貴). This package is based on
      \LaTeXe\ and \emph{fontspec} package.
\item the \emph{luajp-test} package~\cite{luajp-test}, a test package made by
      Atsuhito Kohda (香田温人), based on articles on the web page~\cite{joylua}.
\end{itemize}
However, these packages are based on \LaTeXe, and do not have much
ability to control the typesetting rule. And it is inefficient that more
than one people separately develop similar packages.  Development of the
\LuaTeX-ja package is started initially by the author and Kazuki Maeda, because of
these situations.

\subsection{Development Policy of \LuaTeX-ja}
\label{ssec-pol} 
The first aim of the \LuaTeX-ja project is to implement features (from the
'primitive' level) of p\TeX\ as macros under \LuaTeX, so \LuaTeX-ja is
much affected by p\TeX.  However, as development proceeds, some
technical/conceptual difficulties are arisen. Hence we changed the aim
of the project as follows:
\begin{itemize}
\item\emph{\LuaTeX-ja offers at least the same flexibility of
     typesetting that p\TeX\ has.}

     We think that the ability of producing outputs conformed to
     JIS~X~4051~\cite{jisx4051}, the Japanese Industrial Standard for
     typesetting, or to a technical note~\cite{w3c} by W3C is not enough;
     if one wants to produce very incoherent outputs for some reason, it
     should be possible.
In this point, previous attempts of Japanese typesetting with \LuaTeX\
     which we cited in the previous subsection are inadequate.

p\TeX\ has some flexibility of typesetting, by changing internal
     parameters such as |\kanjiskip| or |\prebreakpenalty|, and by using
     custom JFM (Japanese TFM). 

\item\emph{\LuaTeX-ja isn't mere re-implementation or porting of p\TeX;
     some (technically and/or conceptually) inconvenient features of
     p\TeX\ are modified.} 

     We describe this point in more detail at the next section.
\end{itemize}


\subsection{Contents of this Paper}
Here we describe the contents of the rest of this paper briefly.  In
Section~2, we describe major differences between p\TeX\ and \LuaTeX-ja.
In Section~3, we show the current status of the \LuaTeX-ja package. In
Section~4, we describe some internal routines of \LuaTeX-ja.  We hope
that the materials in this section have good applications.

\subsection*{About the Project}
This \LuaTeX-ja project is hosted by SourceForge.jp. The official wiki
is located on
\url{http://sourceforge.jp/projects/luatex-ja/wiki/FrontPage}.  There is
no stable version at Oct.\ 11, 2011, however the development source can be
obtained from the git repository.  Members of the project are as follows
(in random order): Hironori Kitagawa, Kazuki Maeda, Takayuki Yato,
Yusuke Kuroki, Noriyuki Abe, Munehiro Yamamoto, Tomoaki Honda,
and~Shuzaburo Saito.


\section{Major differences with \pTeX}
In this section, we look at several major differences between p\TeX\
and our \LuaTeX-ja.  For general information of Japanese typesetting and the
overview of p\TeX, please see Okumara~\cite{ptexjp}.


\subsection{Names of Control Sequences}
\label{ssec-csname} Since p\TeX\ is an engine modification of Knuth's
original \TeX82 engine, some primitives added by it take a form that is
very difficult to be simulated by a macro.  For example, an additional
primitive |\prebreakpenalty|$\langle\hbox{\it
char\_code}\rangle$|[=]|$\langle\hbox{\it penalty}\rangle$ in p\TeX\
sets the amount of penalty inserted before a character whose code is
$\langle\hbox{\it char\_code}\rangle$ to $\langle\hbox{\it
penalty}\rangle$, and |\prebreakpenalty|$\langle\hbox{\it
char\_code}\rangle$ can be also used for retrieving the value.

Moreover, there are some parameters which values of them at the end of a
horizontal box or that of a paragraph are effective in whole box or
paragraph.  These parameters were implemented as additional internal
parameters in \pTeX. However, the implementation of these parameters in
\LuaTeX-ja is not so easy; we will discuss on it in
Subsection~\ref{ssec-stack}.

From above 2~problems we discussed above, the assignment and retrieval
of most parameters in \LuaTeX-ja are summarized into the following
3~control sequences:
\begin{itemize}
\item |\ltjsetparameter{|$\langle\hbox{\it
      name}\rangle$|=|$\langle\hbox{\it value}\rangle$|,...}|: for local
      assignment.
\item |\ltjglobalsetparameter|: for global assignment. These two control
      sequences obey the value of |\globaldefs| primitive.
\item |\ltjgetparameter{|$\langle\hbox{\it
      name}\rangle$|}[{|$\langle\hbox{\it optional
      argument}\rangle$|}]|: for retrieval. The returned value is always
      a string.
\end{itemize}

\subsection{Line Break after a Japanese Character}
\label{ssec-line} 

Japanese texts can break lines almost everywhere, in contrast with
alphabetic texts can break lines only between words (or use
hyphenation). Hence, p\TeX's input processor is modified so that a
line break after a Japanese character doesn't emit a space. However,
there is no way to customize the input processor of \LuaTeX, other than
to hack its CWEB-source. All a macro package can do is to modify an input line before
when \LuaTeX\ begin to process it, inside the |process_input_buffer|
callback.

Hence, in \LuaTeX-ja, a comment letter (we reserve U+FFFFF for this
purpose) will be appended to an input line, if this line ends with a Japanese
character\footnote{Strictly speaking, it also requires that the catcode
of the end-line character is 5~(\emph{end-of-line}). This condition is
useful under the verbatim environment.}. One might jump to a conclusion
that the treatment of a line break by p\TeX\ and that of \LuaTeX-ja are
totally same, however they are different in the respect that \LuaTeX-ja's
judgement whether a comment letter will be appended the line is done
\emph{before} the line is actually processed by \LuaTeX.

Figure~\ref{fig-linebreak} shows an example of this situation; the
command at the first line marks most of Japanese characters as
non-Japanese characters. In other words, from that command onward, the
letter `あ' will be treated as an alphabetic character by
\LuaTeX-ja. Then, it is natural to occur a space between `あ' and `y' in
the output, where the actual output in the figure does not so.  This is
because `あ' is considered to be a Japanese character by \LuaTeX-ja,
when \LuaTeX-ja does a decision whether U+FFFFF will be added to the
input line~2.

\begin{figure}
\begin{LTXexample}
\font\x=IPAMincho \x
\ltjsetparameter{jacharrange={-6}}xあ
y
\end{LTXexample}
\caption{A notable sample showing the treatment of a line break after a
Japanese character.}\label{fig-linebreak}
\end{figure}

\subsection{Separation between `real' fonts and Metrics}
\label{ssec-sepmet}

Traditionally, most Japanese fonts used in typesetting are not
proportional, that is, most glyphs have same size (in most cases,
square-shaped). Hence, it is not rare that the contents of different
JFMs are totally same, and only differ in their names. For example,
|min10.tfm| and |goth10.tfm|, which are JFMs shipped with p\TeX\ for
seriffed \emph{mincho} family and sans-seriffed \emph{gothic} family,
differ their |FAMILY| and |FACE| only. Moreover, |jis.tfm| and
|jisg.tfm|, which consists a parts of \emph{jis} font metric, which is
used in \emph{jsclasses}~\cite{jsclasses} by Haruhiko Okumura (奥村晴彦),
are totally same as binary files.  Considering this situation, we
decided to separate `real' fonts and metrics used for them in
\LuaTeX-ja. Typical declarations of Japanese fonts in the style of plain
\TeX\ are shown in Figure~\ref{fig-jfdef}.
\begin{itemize}
\item A control sequence |\jfont| must be used for Japanese fonts, instead of |\font|.
\item \LuaTeX-ja automatically loads the \emph{luaotfload} package, so
      |file:| and |name:| prefixes, and various font features can be
      used as the line~1 in Figure~\ref{fig-jfdef}.
\item The |jfm| key specifies the metric for the font. In
      Figure~\ref{fig-jfdef}, both fonts will use a metric stored in a
      Lua script named |jfm-ujis.lua|. This metric is the standard
      metric in \LuaTeX-ja, and is based on JFMs used in the \emph{otf}
      package~\cite{otf}.
\item The |psft:| prefix can be used to specify name-only, non-embedded
      fonts. When one display a pdf with these fonts, actual fonts which
      will be used for them depend on a pdf reader. 
\end{itemize}
The specification of a metric used in \LuaTeX-ja is similar to that of a
JFM (see \cite{ptexjp}); characters are grouped into several classes,
the size information of characters are specified for each class, and
glue/kern insertions are specified for each pair of classes. Although
the author have not tried, it may be possible to develop a program that
`converts' a JFM to a metric for \LuaTeX-ja.  \LuaTeX-ja offers three
metrics by default; |jfm-ujis.lua|, |jfm-jis.lua| based on the
\emph{jis} font metric, and |jfm-min.lua| based on old |min10.tfm|.

 Note that |-kern| in features
is important, since  kerning information from real font itself will
clash with glue/kern informations from the metric.

\begin{figure}
\begin{verbatim}
\jfont\foo=file:ipam.ttf:jfm=ujis;script=latn;-kern;+jp04 at 12pt
\jfont\bar=psft:Ryumin-Light:jfm=ujis at 10pt
\end{verbatim}
\caption{Typical declarations of Japanese fonts.}
\label{fig-jfdef}
\end{figure}

\subsection{Insertion of Kerns and/or Glues for Japanese Typesetting: the Timing}
\label{ssec-jglue}

As described in \cite{luatexref}, \LuaTeX's kerning and ligaturing
processes are totally different from those of \TeX82.  \TeX82's process is
done just when a (sequence of) character is appended to current
list. Thus we can interrupt this process by writing as
|f{}irm|. However, \LuaTeX's process is \emph{node-based}, that is, the
process will be done when a horizontal box or a paragraph is ended, so
|f{}irm| and |firm| yield  same outputs under \LuaTeX.

The situation for Japanese characters is more complicated.
Glues (and kerns) which are needed for Japanese
typesetting will be divided into the following three categories:
\begin{itemize}
\item Glue (or kern) from the metric of Japanese fonts (\emph{JFM glue},
      for short). 

\item Default glue between a Japanese character and an alphabetic
      character (\emph{xkanjiskip}, for short), usually 1/4 of
      full-width (\emph{shibuaki}) with some stretch and shrink for
      justifying each line.
\item Default glue between two consecutive Japanese characters
      (\emph{kanjiskip}, for short). The main reason of this glue is to
      enable breaking lines almost everywhere in Japanese texts. In most
      cases, its natural width is zero, and some stretch/shrink for
      justifying each line.
\end{itemize}
In p\TeX, these three kinds of glues are treated differently. A JFM glue
is inserted when a (sequence of) Japanese character is appended to
current list, same as the case of alphabetic characters in \TeX82. This
means that one can interrupt the insertion process by saying |{}|.  A
\emph{xkanjiskip} is inserted just before `hpack' or line-breaking of a
paragraph; this timing is somewhat similar to that of \LuaTeX's kerning
process. Finally, A \emph{kanjiskip} is not appeared as a node anywhere;
only appears implicitly in calculation of the width of a horizontal box,
that of breaking lines, and the actual output process to a DVI
file. These specifications made p\TeX's behavior very hard to
understand.

\LuaTeX-ja inserts glues in all three categories simultaneously inside
|hpack_filter| and |pre_linebreak_filter| callbacks.  The reasons of
this specification are to behave like alphabetic characters in \LuaTeX\
(as described in the first paragraph), and to clarify the specification
for \LuaTeX-ja's process.

\subsection{Insertion of Kerns and/or Glues for Japanese Typesetting: the Spec}
\begin{table}
\caption{Examples of differences between  p\TeX\ and \LuaTeX-ja,}
\label{tab-jfmglue}
\begin{center}
\begin{tabular}{llllllll}
\toprule
&\multicolumn{1}{c}{(1)}&\multicolumn{1}{c}{(2)}&\multicolumn{1}{c}{(3)}&\multicolumn{1}{c}{(4)}\\
Input      &|あ】{}【〙\/〘|        &|い』\/a| &|う）\hbox{}（| &|え］\special{}［|\\\midrule
p\TeX      &あ】\hbox{}【〙\hbox{}〘&い』\/a   &う）\hbox{}（   &え］\hbox{}［\\
\LuaTeX-ja &あ】{}【〙\/〘          &い』\/a   &う）\hbox{}（   &え］\special{}［\\
\bottomrule
\end{tabular}
\end{center}
\end{table}

\begin{figure}
\begin{center}
\fontsize{40}{40}\selectfont
\imagfm{\jstrut あ}%
\imagfm{\jstrut 】\inhibitglue}%
\imagfm{\jstrut\kern.5\zw}%
\imagfm{\jstrut\kern.5\zw}%
\imagfm{\jstrut\inhibitglue【}%
\imagfm{\jstrut 〙\inhibitglue}%
\imagfm{\jstrut\kern.5\zw}%
\imagfm{\jstrut\kern.5\zw}%
\imagfm{\jstrut\inhibitglue〘}%
\end{center}
\caption{Detail of (1) in Table~\ref{tab-jfmglue}.}
\label{fig-ptexjfm}
\end{figure}

Now we will take a look inside the insertion process itself, and describe 4~points.

\begin{description}
\item[Ignored Nodes]
As noted in the previous subsection, the insertion process in p\TeX\ can be
           interrupted by saying |{}| or anything else\footnote{This is
           why some tricks like \texttt{ちょ\char`\{\char`\}っと} that
           are needed when we use \texttt{min10.tfm} work.}. This leads
           the second row in Table~\ref{tab-jfmglue}, or
           Figure~\ref{fig-ptexjfm}. `The process is interrupted' means
           that p\TeX\ does not think the letter `】\inhibitglue' is
           followed by `\inhibitglue【', hence two half-width glues are
           inserted between between `】\inhibitglue' and `\inhibitglue【',
           where one is from `】\inhibitglue' and another is from
           `\inhibitglue【'.

           On the other hand, in \LuaTeX-ja, the process is done inside
           |hpack_filter| and |pre_linebreak_filter| callbacks. Hence,
           \emph{anything that does not make any node will be
           ignored}\ in \LuaTeX-ja, as shown in (1) in
           Table~\ref{tab-jfmglue}. \LuaTeX-ja also ignores any nodes
           which does not make any contribution to current horizontal
           list---\emph{ins\_node}, \emph{adjust\_node},
           \emph{mark\_node}, \emph{whatsit\_node} and
           \emph{penalty\_node}---, as shown in (4).

By the way, around a \emph{glyph\_node} $p$ there may be some nodes
           attached to $p$. These are an accent and kerns for
           positioning it, and a kern from italic
           correction\footnote{\TeX82 (and \LuaTeX) does not distinguish
           between explicit kern and a kern for italic correction. To
           distinguish them, \LuaTeX-ja uses an additional attribute and
           redefines \texttt{\char`\\/}.} for $p$. It is natural that
           these attachments should be ignored in the process. Hence
           \LuaTeX-ja takes this approach, as the latest version of
           p\TeX\ (p3.2). This explains (2) in the figure.

Summerizing above, one should put an empty horizontal box |\hbox{}| to
           where he wants to interrupt the insertion process in
           \LuaTeX-ja as (3) in the figure.

\item[Fonts with the Same Metric]
Recall that \LuaTeX-ja separated `real' fonts and metrics, as in Subsection~\ref{ssec-sepmet}. 
Consider the following input, where all Japanese fonts use same metric
           (in \LuaTeX-ja), and |\gt| selects \emph{gothic} family for
           the current Japanese font family:
\begin{quote}
\begin{verbatim}
明朝）\gt （ゴシック
\end{verbatim}
\end{quote}
If the above input is processed by p\TeX, since the insertion process is
           interrupt by |\gt|, the result looks like
\begin{quote}
\mc 明朝）\hbox{}\gt （ゴシック
\end{quote}
However this seems to be unnatural, since two Japanese fonts in the
           output uses the same metric, \emph{i.e.}, the same
           typesetting rule.  Hence, we decided that Japanese fonts with
           the same metric are treated as one font in the insertion
           process of \LuaTeX-ja. Thus, the output from the above input
           in \LuaTeX-ja is:
\begin{quote}
\mc 明朝）\gt （ゴシック
\end{quote}
One might have the situation that this default behavior is not
           suitable. \LuaTeX-ja offers a way to cope with this case, but
           we leave it to the manual~\cite{man}.

\item[Fonts with Different Metrics] 
In the case where two consecutive Japanese characters use different metrics and/or
           different size is similar. Consider the following input where
           the \emph{mincho} family and the \emph{gothic} family use
           different metrics:
\begin{quote}
\begin{verbatim}
漢）\gt （漢）\large （大
\end{verbatim}
\end{quote}
As the previous paragraph, this input yields the following, by p\TeX:
\begin{quote}
\mc 漢）\hbox{}\gt （漢）\hbox{}\large （大
\end{quote}
We thought that amounts of spaces between parentheses in above output
           are too much. So we changed the default behavior of
           \LuaTeX-ja so that the amount of a glue between two Japanese
           characters with different metrics is the average of a glue
           from the left character and that from the right
           character. For example, Figure~\ref{fig-diffmet} shows the
           output from above input. The width of glue indicated `(1)' is
           $(a/2 + a/2)/2 = 0.5a$, and the width of glue indicated `(2)'
           is $(a/2 + 1.2a/2)/2 = 0.55a$. This default behavior can be
           changed by \textsf{diffrentmet} parameter of \LuaTeX-ja.

\begin{figure}
\begin{center}
\fontsize{40}{40}\selectfont
\imagfm{\jstrut\smash{%
  \vtop{\lineskiplimit=\maxdimen\lineskip2pt\halign{#\cr漢\cr
    \small\vrule height .5ex depth .5ex\hrulefill\ \lower.5ex\hbox{$a$}\ 
    \hrulefill\vrule height .5ex depth .5ex\cr}}}}%
\imagfm{\jstrut ）\inhibitglue}%
\imagfm{\jstrut\hbox to .5\zw{\hss\normalsize (1)\hss}}%
\imagfm{\jstrut\inhibitglue\gt （}%
\imagfm{\jstrut\gt 漢}%
\imagfm{\jstrut\gt ）\inhibitglue}%
\imagfm{\jstrut\hbox to .55\zw{\hss\normalsize (2)\hss}}%
\imagfm{\fontsize{48}{48}\selectfont\jstrut\gt\inhibitglue （}%
\imagfm{\fontsize{48}{48}\selectfont\jstrut\smash{%
  \vtop{\lineskiplimit=\maxdimen\lineskip2pt\halign{#\cr\gt 大\cr
    \small\vrule height .5ex depth .5ex\hrulefill\ \lower.5ex\hbox{$1.2a$}\ 
    \hrulefill\vrule height .5ex depth .5ex\cr}}}}
\end{center}
\caption{Fonts with different metrics.}
\label{fig-diffmet}
\end{figure}

\item[\emph{kanjiskip} and \emph{xkanjiskip}]
In p\TeX, the value of \emph{xkanjiskip} is controlled by a skip named
           |\xkanjiskip|. A defect of this implementation is that the
           value of \emph{xkanjiskip} is not connected with the size of
           the currnt Japanese font. It seems that |EXTRASPACE|,
           |EXTRASTRETCH|, |EXTRASHRINK| parameters in a JFM are
           reserved for specifying the default value of
           \emph{xkanjiskip} in a unit of the design size, but p\TeX\
           did not use these parameters. 

Considering this situation of p\TeX, \LuaTeX-ja can use the value of
           \emph{xkanjiskip} that specified in a metric. If the value of
           \emph{xkanjiskip} on the user side (this is the
           \textsf{xkanjiskip} parameter in |\ltjsetparameter|) is
           |\maxdimen|, then the \LuaTeX-ja use the specification from
           the current used metric as the actual value of
           \emph{xkanjiskip}.
This description also applies for \emph{kanjiskip}.
\end{description}


\section{Current Status of Development}
At the moment, \LuaTeX-ja can be used under plain \TeX, and under
\LaTeXe. Generally speaking, one only has to read |luatexja.sty|, by |\input|
command or |\usepackage| (in~\LaTeXe), if you merely want to typeset
Japanese character.  We look more detail by parts.

\subsection{`Engine Extension'}
The lowest part of \LuaTeX-ja corresponds the p\TeX\ extension as
\emph{an engine extension of \TeX}. We, the project menbers, think that
this part is almost done. Other features of \LuaTeX-ja which we have not
described are the followings:
\begin{description}
\item[Setting the Range of `Japanese characters'] This feature is
           inspired by up\TeX. up\TeX\ has an additional primitive named
           |\kcatcode| for setting how a character is treated among an
           alphabetic character, \emph{kana}, \emph{kanji},
           \emph{Hangul}, or~\emph{an other CJK character}. and the
           assignment of |\kcatcode| can be done by a Unicode
           block\footnote{There are some exceptions. For example,
           U+FF00--FFEF (Halfwidth and Fullwidth Forms) are divided into
           three blocks in up\TeX.}.

\LuaTeX-ja uses a slightly different approach. Because there are many
           Unicode blocks already in Basic Multilingual Plane which are
           not included in most Japanese fonts, so it would be
           inefficient to toggle by a Unicode block.  Furthermore, the
           basic Japanese character set JIS~X~0208 are not just union of
           Unicode blocks; for example, the intersection of JIS~X~0208
           and Latin-1 Supplement is shown in Table~\ref{tab-inter}.
           Considering these two points, to customize the range of
           Japanese characters in \LuaTeX-ja, one has to define
           character ranges in his source in advance.

\item[Shifting Baseline]
In order to make a match between Japanese fonts and alphabetic fonts,
           sometimes shifting the baseline of alphabetic characters may
           be needed. p\TeX\ has a dimension |\ybaselineshift|, which
           corresponds the amount of shifting down the baseline of alphabetic
           characters. This is useful for Japanese-based documents, but
           not for documents mainly in languages with alphabetic
           characters.

Hence, \LuaTeX-ja extends p\TeX's |\ybaselineshift| to Japanese
           characters. Namely, \LuaTeX-ja offers two parameters,
           \textsf{yjabaselineshift} and \textsf{yalbaselineshift}, for the
           amount of shifting the baseline of Japanese characters and
           that of alphabetic characters, respectively. 

\begin{figure}
\begin{center}
\fontsize{40}{40}\selectfont\fboxsep0mm
\vrule width 0.9\textwidth height0.4pt depth0.4pt\kern-0.9\textwidth
\hbox to 0.9\linewidth{%
\hfil
\raise-10pt\imagfm{\jstrut 漢}%
\raise-10pt\imagfm{\jstrut 字}\hskip.25\zw%
\imagfm{p}%
\imagfm{h}%
\hfil\hfil
\imagfm{\jstrut 漢}%
\imagfm{\jstrut 字}\hskip.25\zw%
\raise-10pt\imagfm{p}%
\raise-10pt\imagfm{h}%
\hfil
}
\end{center}

\caption{First example of shifting baseline.}
\label{fig-bls}
\end{figure}

\begin{figure}
\begin{center}
\fontsize{30}{30}\selectfont\fboxsep0mm
\vrule width 0.9\textwidth height0.4pt depth0.4pt\kern-0.9\textwidth
\hbox to 0.9\linewidth{%
\hfil
\imagfm{a}%
\imagfm{b}\hskip.25\zw%
\imagfm{\jstrut 本}%
\imagfm{\jstrut 文}\hskip.33333\zw%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont\jstrut\inhibitglue （}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont\jstrut 注}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont\jstrut 釈}\hskip.1666667\zw%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont c}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont o}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont m}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont m}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont e}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont n}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont t}%
\raise3.514582pt\imagfm{\fontsize{20}{20}\selectfont\jstrut ）\inhibitglue}%
\hskip.33333\zw%
\imagfm{\jstrut 本}%
\imagfm{\jstrut 文}%
\hfil
}
\end{center}

\caption{Second example of shifting baseline.}
\label{fig-small}
\end{figure}

An example output is shown in Figure~\ref{fig-bls}. The left half is the
           output when \textsf{yjabaselineshift} is positive, hence the
           baseline of Japanese characters is shifted down. On the other
           hand, the right half is the output when
           \textsf{yalbaselineshift} is positive, hence the baseline of
           alphabetic characters is shifted. Figure~\ref{fig-small}
           shows an intresting use of these parameters.

\end{description}
Note that \LuaTeX-ja doesn't support for vertical typesetting, \emph{tategaki}, for now. 

\begin{table}
\caption{Intersection of JIS~X~0208 and Latin-1 Supplement.}
\label{tab-inter}
\begin{center}
\begin{tabular}{llll}
\char"A7 (U+00A7),&
\char"A8 (U+00A8),&
\char"B0 (U+00B0),&
\char"B1 (U+00B1),\\
\char"B4 (U+00B4),&
\char"B6 (U+00B6),&
\char"D7 (U+00B7),&
\char"F7 (U+00D7)
\end{tabular}
\end{center}
\end{table}

\subsection{Patches for plain \TeX\ and \LaTeXe}
p\TeX\ has a patch for plain \TeX, namely |ptex.tex|, that for \LaTeXe\
macro (this patch and \LaTeXe\ consist \emph{p\LaTeXe}), and
|kinsoku.tex| which includes the default setting of \emph{kinsoku
shori}, the Japanese hyphenation.  We ported them to \LuaTeX-ja, except
the codes related to vertical typesetting, since \LuaTeX-ja doesn't
support vertical typesetting yet. We remark two points related to the
porting:
\begin{description}
\item[Default Range of Japanese Characters] 
As described in the previos subsection, \LuaTeX-ja can customize the
range of Japanese characters.  \LuaTeX-ja predefines 8~character ranges,
as shown in Table~\ref{tab-chrrng}.  Almost of these ranges are just the
union of Unicode blocks, and determined from the Adobe-Japan1-6 character
correction, and JIS~X~0208.  And, among these 8~ranges, the ranges~2, 3, 6, 7,
and~8 are considered ranges of Japanese characters, and others are
considered ranges of alphabetic characters.

This default setting is suitable for Japanese-based documents, however it
           causes that other packages which use Unicode fonts do not work
           correctly. For example, |\times| provided by the
           |unicode-math| package is the character U+00D7, which belongs
           to the range~8, and |\textendash| provided by the |EU2|
           encoding used in the \emph{fontspec} package is the
           character U+2013, which belongs to the range~3. hence, these
           charatcer cannot be typeset with the default range setting.

\begin{table}
\caption{Predefined ranges in \LuaTeX-ja}
\label{tab-chrrng}
\begin{center}
\begin{tabular}{@{\bf}rl}
1&(Additional) Latin characters which is not belonged in the range~8.\\
2&Greek and Cyrillic letters.\\
3&Punctuations and miscellaneous symbols.\\
4&Unicode blocks which does not intersect with Adobe-Japan1.\\
5&Surrogates and supplementary private use Areas.\\
6&Characters used in Japanese typesetting.\\
7&Characters possibly used in CJK typesetting, but not in Japanese.\\
8&Characters in Table~\ref{tab-inter}.
\end{tabular}
\end{center}
\end{table}


\item[Behavior of\/ {\tt\char92fontfamily\/}]
The control sequence |\fontfamily| in p\LaTeXe\ changes the current alphabetic
           font family and/or the current Japanese font family,
           depending the argument. More concretely,
           |\fontfamily{|$\langle\hbox{\it arg\/}\rangle$|}| changes the
           current alphabetic font family to $\langle\hbox{\it
           arg\/}\rangle$, if and only if one of the following
           conditions are satisfied:
\begin{itemize}
\item An alphabetic font family named $\langle\hbox{\it arg\/}\rangle$ in
      \emph{some} alphabetic encoding already defined in the document.
\item There exists an alphabetic encoding $\langle\hbox{\it
      enc\/}\rangle$ already defined in the document such that a font
      definition file $\langle\hbox{\it enc\/}\rangle\langle\hbox{\it
      arg\/}\rangle$|.fd| exists.
\end{itemize}
The same criterion is used for changing Japanese font family.

To work this behavior well, a list of all encodings defined already in the
           document is needed. Since \LuaTeX-ja is loaded as a package,
           \LuaTeX-ja cannot have this list.  Hence \LuaTeX-ja adopted different
           approach, namely |\fontfamily{|$\langle\hbox{\it
           arg\/}\rangle$|}| changes the current alphabetic font family
           to $\langle\hbox{\it arg\/}\rangle$, if and only if:
\begin{itemize}
\item An alphabetic font family named $\langle\hbox{\it arg\/}\rangle$ in
      the current alphabetic encoding $\langle\hbox{\it enc\/}\rangle$.
\item A  font definition file $\langle\hbox{\it enc\/}\rangle\langle\hbox{\it
      arg\/}\rangle$|.fd| exists.
\end{itemize}


\end{description}



\subsection{Classes for Japanese Documents}
To produce `high-quality' Japanese documents, we need not only that
Japanese characters are correctly placed, but also class files for
Japanese documents. In p\TeX, there are two major families of classes:
\emph{jclasses} which is distributed with the official p\LaTeXe\ macros,
and \emph{jsclasses}.  At the present, \LuaTeX-ja
simply contains their counterparts: \emph{ltjclasses} and
\emph{ltjsclasses}. However, the policy on classess is not determined
now, and we hope to have another family of classes which are useful in
commercial printing.  In the author's opinion, \emph{ltjclasses} is
better to stay as an example of porting of class files for \pTeX\ to
\LuaTeX-ja.

\subsection{Patches for Packages}
Apart from patches for the \LaTeXe~kernel and classes for Japanese
documents, we need to make patches for several packages. At the present,
we considered the following packages, and made patches or porting for
the former two packages.

\begin{description}
\item[The \emph{fontspec} package] The \emph{fontspec} package is built
           on NFSS2, hence control sequences offered by the
           \emph{fontspec} package, such as |\setmainfont|, are only
           effective for alphabetic fonts if \LuaTeX-ja is
           loaded. |luatexja-fontspec.sty| offers these counterparts for
           Japanese fonts, with additional `j' in the name of control
           sequences, such as |\setmainjfont|.

\item[The \emph{otf} package]
This package is widely used for characters which is
not in JIS~X~0208, and for using more than one weight in \emph{mincho}
and \emph{gothic} font families. Therefore \LuaTeX-ja supports features
in the \emph{otf} package, by loading |luatexja-otf.sty|. Note that
characters by |\UTF{xxxx}| and |\CID{xxxx}| are not appended to the
current list as a \emph{glyph\_node}, so they are not affected by
callbacks by the \emph{luaotfload} package. We have another remark; |\CID| does not work
with TrueType fonts.

\item[The \emph{listings} package]
It is well-known that there is a patch of the \emph{listings} package for
           p\LaTeXe,\ called |jlisting.sty|. Generally speaking, it also
           can be used in \LuaTeX-ja. However, it seems to be that a
           Japanese character after a space does not recieve any process
           of the \emph{listings} package; this is inconvinient when we
           use the \emph{showexpl} package.
\end{description}



\section{Implementation}
\subsection{Handling of Japanese Fonts}
In p\TeX, there are three slots for maintaining current fonts, namely
|\font| for alphabetic fonts, |\jfont| for Japanese font (in horizontal
direction) and |\tfont| for Japanese font (in vertical direction). With
these slots, we can manage the current font for alphabetic characters
and that for Japanese characters separately in p\TeX.  However, \LuaTeX\
has only one slot for maintaining the current font, as \TeX82.  This
situation leads a problem: how can we maintain the `current Japanese
font'?

There are three approaches for this problem. One approach is to make a
mapping table from alphabetic fonts to corresponding Japanese fonts
(here we don't assume that NFSS2 is available).  Another approach is
that we always use composite fonts with alphabetic fonts and Japanese
fonts. The third approach is that the information of the current
Japanese font is stored in an attribute. We adopted the third approach,
since \LuaTeX-ja is much affected by p\TeX\ as we noted in
Subsection~\ref{ssec-pol}.

As in Figure~\ref{fig-jfdef}, \LuaTeX-ja uses |\jfont| for defining
Japanese font, as p\TeX.  However, since the information of the current
Japanese font is stored into an attribute, control sequences defined by
|\jfont| (\emph{e.g.},~|\foo| and |\bar| in Figure~\ref{fig-jfdef}) is
not representing a font by the means of \TeX82. In other words, each of
these control sequences is just an assignment to an attribute, therefore
they cannot be an argument of |\the|, |\fontname|, or |\textfont|.

\subsection{Overview of the Processes}
Now we describe an outline of the \LuaTeX-ja's process briefly.
\begin{description}
\item[Treatment of Linebreaks after Japanese Characters] This part is
           described already in Subsection~\ref{ssec-line}. Done in the
           |process_input_buffer| callback.
\item[Font Replacement] In the |hyphenate| callback, \LuaTeX-ja looks
           into for each \textit{glyph\_node}~$p$ in the list. If the
           character represented by $p$ is considered as a Japanese
           character, the font used in $p$ is replaced by the value of
           |\ltj@curjfnt|, `the current Japanese font' at~$p$. Also the
           character class of the character is looked up at this time.

Furthermore the subtype of $p$ is subtracted by 1 to suppress
           hyphenation around it by \LuaTeX, since later processes of
           \LuaTeX-ja take care of all things about Japanese charaters.
\end{description}
%
Following processes are all executed in |pre_linebreak_filter| and
|hpack_filter| callback. These processes are main routines of \LuaTeX-ja.

\begin{description}
\item[Examination of Stack Level] The horizontal list which
           is the content of a horizontal box is traversed, 
to determine what is the level of \LuaTeX-ja's internal stack at the end
           of the list. This is needed because of the place of
           |hpack_filter| callback in the source of \LuaTeX. We will discuss more
           detail in Subsection~\ref{ssec-stack}.

\item[Insertion of Glues/Kerns for Japanese Typesetting]
This part is already described at Subsection~\ref{ssec-jglue}. 

\item[Adjustument of the Position of (Japanese) Characters]
We will discuss the detail about this in Subsection~\ref{ssec-width}.
\end{description}

The callbacks by the \emph{luaotfload} package, e.g., replacement of
glyphs according to font features, are executed just after `Examination
of Stack Level' above. 

\subsection{Stack Management}
\label{ssec-stack}

As we noted in Subsection~\ref{ssec-csname}, parameters that the values
at the end of a horizontal box or that of a paragraph are effective in
whole box or paragraph, such as \emph{kanjiskip}, cannot be implemented
by internal integers or registers of other types in \TeX. We explain it
in this section.

\begin{figure}
\begin{lstlisting}
void package(int c)
{
    ...
    d = box_max_depth;
    unsave();
    save_ptr -= 4;
    if (cur_list.mode_field == -hmode) {
        cur_box = filtered_hpack(cur_list.head_field,
                                 cur_list.tail_field, saved_value(1),
                                 saved_level(1), grp, saved_level(2));
        subtype(cur_box) = HLIST_SUBTYPE_HBOX;
    } else {
\end{lstlisting}
\caption{An extract of a CWEB-source \texttt{tex/packaging.w} of \LuaTeX}
\label{fig-ltsrc}
\end{figure}

Figure~\ref{fig-ltsrc} is an extract of a CWEB-source
\texttt{tex/packaging.w} of \LuaTeX\ (SVN revision 4358). This function
is called just when explicit |\hbox{...}| or |\vbox{...}| is ended, and
the function |filtered_hpack()| is where the |hpack_filter| and then the
actual `hpack' process are performed. Notice that the |unsave()|
function is called before |filtered_hpack()|. This is the problem;
because of |unsave()|, we can retrive only the values of registers
\emph{outside} the box, even in the |hpack_filter| callback.

To cope with this problem, \LuaTeX-ja has its own stack system, based on
Lua codes in \cite{stack-mail}. Furthermore, \emph{whatsit} nodes whose
\emph{user\_id} is 30112 (\emph{stack\_node}, for short) will be
appended to the current horizontal list each time the current stack
level is incremented, and their values are the values of
|\currentgrouplevel| at that time. In the beginning of |hpack_filter|
callback, the list in question is traversed to determine whether the
stack level at the end of the list and that outside the box coincides.

Let $x$ be the value of |\currentgrouplevel|, and $y$ be the current
stack level, both inside the |hpack_filter| callback, i.e., outside a
horizontal box. Consider a list which represents the content of the box,
then we have:
\begin{itemize}
\item A \emph{stack\_node} whose value is $x+1$ (since all materials in
      the box are included in a group |\hbox{...}|, the value is at
      least $x+1$) in the list represents an assignment related to the
      stack system in just top-level of the list, like
\begin{quote}
\begin{verbatim}
\hbox{...(assignment)...}
\end{verbatim}
\end{quote}
In this case, the current stack level is incremented to $y+1$ after the assignment.
\item A \emph{stack\_node} whose value is more than  $x+1$ in the list represents
an assignment inside another group contained in the box. For example,
      the following input creates
a \emph{stack\_node} whose value is $x+3=(x+1)+2$:
\begin{quote}
\begin{verbatim}
\hbox{...{...{...(assignment)}...}...}
\end{verbatim}
\end{quote}
\end{itemize}
Thus, we can conclude that the stack level at the end of the list is
$y+1$, if and only if there is a \emph{stack\_node} whose value is
$x+1$. Otherwise, the stack level is just $y$.

\subsection{Adjustment of the Position of Japanese Characters}
\label{ssec-width}

The size of a glyph specified in a metric and that of the real font
usually differ. For example, the letter `\inhibitglue【' is half-width
in |jfm-ujis.lua| or |jis.tfm|, while this letter is full-width like `【'
in most TrueType fonts used in Japanese typesetting, such as
IPA~Mincho. Hence the adjustment of position of such glyphs is
needed. In the context of p\TeX, this process was performed using virtual fonts.

On the other hand, Lua\TeX-ja does the adjustment by encapsuling a glyph
into a horizontal box. There are two main reasons why we adopted this
method; one is that we feared Lua codes for coexisting with callback by
|luaotfload| package would be large if we use virtual fonts, and the
other is to cope with the shifting of the baseline of characters at the
same time. 

\begin{figure}
\begin{center}\unitlength=9pt\small
\begin{picture}(15,12)(-1,-3)

\color{gray10}% real glyph
\put(-1,-1.5){\vrule width 6\unitlength height 7\unitlength depth 2.5\unitlength}

\color{black}% real glyph :step1
\thicklines
\put(-1,-1.5){\line(0,1){7}\line(0,-1){2.5}}
\put(5,-1.5){\line(0,1){7}\line(0,-1){2.5}}
\put(-1,5.5){\line(1,0){6}}
\put(-1,-4){\line(1,0){6}}

\thicklines
\put(0,0){\vector(0,1){9}\line(0,-1){3}\vector(1,0){12}}
\put(12,9){\makebox(0,0)[rt]{\strut$M$\,}}
\put(12,0){\line(0,1){9}\vector(0,-1){3}}
\put(0,9){\line(1,0){12}}
\put(0,-3){\line(1,0){12}}
\put(0.2,4.5){\makebox(0,0)[l]{\texttt{height}}}
\put(12.2,-1.5){\makebox(0,0)[l]{\texttt{depth}}}
\put(6,0.2){\makebox(0,0)[b]{\texttt{width}}}

\thicklines
\put(3,0){\line(0,1){7}\line(0,-1){2.5}\line(1,0){6}}
\put(9,0){\line(0,1){7}\line(0,-1){2.5}}
\put(3,7){\line(1,0){6}}
\put(3,-2.5){\line(1,0){6}}
\newsavebox{\eqdist}
\savebox{\eqdist}(0,0)[c]{%
  \thinlines
  \put(-0.08,0.2){\line(0,-1){0.4}}%
  \put(0.08,0.2){\line(0,-1){0.4}}}
\put(1.5,0){\usebox{\eqdist}}
\put(10.5,0){\usebox{\eqdist}}

\thicklines
\put(3,-1.5){\vector(-1,0){4}}
\put(1,-1.7){\makebox(0,0)[t]{\texttt{left}}}
\put(3,0){\vector(0,-1){1.5}}
\put(3.2,-0.75){\makebox(0,0)[l]{\texttt{down}}}
\end{picture} 
\end{center}
\caption{The position of the `real' glyph.}
\label{fig-pos}
\end{figure}

Figure~\ref{fig-pos} shows the adjustment process. A large square $M$ is
the imaginary body which is specified in the metric, and a vertical
rectangle is the imaginary body of a real glyph. First, the real glyph
is aligned with respect to the width of $M$. In the figure, the real
glyph is aligned `middle'; this setting is useful for the full-width
middle dot `・'. We have other settings, namely, `left' and `right'.
After that, it is shifted according to the value of |left| and |down|,
which are specified in the metric. The final position of the real glyph
is shown by the gray rectangle. If the amount of shifting baseline is
not zero, $M$ (and hence the real glyph) is shifted by that amount.

We would like to remark briefly about the vertical position of a glyph.
A JFM (or the metric used in \LuaTeX-ja) and the real font used for it
may have different height or depth.  In that case, it may look better if
the real glyph is shifted vertically to match the height-depth ratio
specified in the metric. This situation is carefully studied by
Otobe~\cite{min10}. Here the policy on this problem is not determined
now, however we want to offer several solutions by \LuaTeX-ja.

\section{Conclusion}
We have discussed about our \LuaTeX-ja package, which is much affected
by p\TeX. For now, it can be used for experimental use, however there
are much refinements which are needed for regular use. The author hopes
that this paper and this project contribute the typesetting Japanese,
and possibly other Asian languages, under \LuaTeX.



%%% The style of the bibiliogrphy is `amsplain'.
\providecommand{\bysame}{\leavevmode\hbox to3em{\hrulefill}\thinspace}
\providecommand{\href}[2]{#2}
\begin{thebibliography}{99}

\bibitem{ptex}
ASCII MEDIA WORKS，アスキー日本語\TeX\ (p\TeX)．\url{http://ascii.asciimw.jp/pb/ptex/}

\bibitem{omega}
Jin-Hwan~Cho and Haruhiko Okumura, \emph{Typesetting CJK Languages with Omega},
\TeX, XML, and Digital Typography, Lecture Notes in Computer Science, vol.~3130,
Springer, 2004, 139--148.

\bibitem{joylua}
Yannis Haralambous. \emph{The Joy of \LuaTeX}. \url{http://luatex.bluwiki.com/}

\bibitem{jisx4051}
Japanese Industrial Standards Committee. \emph{JIS~X~4051: Formatting
        rules for Japanese documents}, 1993, 1995, 2004.

\bibitem{eptex}
北川弘典，$\varepsilon$-p\TeX についてのwiki．
\url{http://sourceforge.jp/projects/eptex/wiki/FrontPage}

\bibitem{luaums}
北川弘典，\LuaTeX で日本語．
\url{http://oku.edu.mie-u.ac.jp/tex/mod/forum/discuss.php?d=378}

\bibitem{luatexref}
\LuaTeX\ development team, \emph{The \LuaTeX\ reference}. 
\url{http://www.luatex.org/svn/trunk/manual/luatexref-t.pdf} (snapshot of SVN trunk)

\bibitem{man}
The \LuaTeX-ja project team, \emph{The \LuaTeX-ja package}. 
Not completed for now. Available at |doc/man-en.pdf| (in English) or
        |doc/man-ja.pdf| (in Japanese)
in the Git repository.

\bibitem{luajp-test}
香田温人，\LuaTeX と日本語．
\url{http://www1.pm.tokushima-u.ac.jp/~kohda/tex/luatex-old.html}

\bibitem{luajalayout}
前田一貴，luajalayout パッケージ---Lua\LaTeX によ
        る日本語組版---．
\url{http://www-is.amp.i.kyoto-u.ac.jp/lab/kmaeda/lualatex/luajalayout/}

\bibitem{jsclasses}
奥村晴彦，p\LaTeXe 新ドキュメントクラス．
\url{http://oku.edu.mie-u.ac.jp/~okumura/jsclasses/}

\bibitem{ptexjp}
Haruhiko Okumura, \emph{p\TeX\ and Japanese Typesetting},
        The Asian Journal of \TeX\ \textbf{2}~(2008), 43--51.

\bibitem{min10}
乙部厳己，min10フォントについて．
\url{http://argent.shinshu-u.ac.jp/~otobe/tex/files/min10.pdf}

\bibitem{otf}
齋藤修三郎，Open Type Font用VF．
\url{http://psitau.kitunebi.com/otf.html}

\bibitem{stack-mail}
Jonathan Sauer, \emph{[Dev-luatex] tex.currentgrouplevel}. 
\url{http://www.ntg.nl/pipermail/dev-luatex/2008-August/001765.html}

\bibitem{uptex}
Takuji Tanaka, \emph{up\TeX, up\LaTeX---unicode version of p\TeX, p\LaTeX}.
\url{http://homepage3.nifty.com/ttk/comp/tex/uptex_en.html}

\bibitem{ptexenc}
Nobuyuki Tsuchimura, \emph{Development of a Japanese \TeX\ Distribution~`ptetex3'},
Computer Software\ \textbf{24} (2007), no.~4, 40--50, (in Japanese).

\bibitem{w3c}
W3C Working Group, \emph{Requirements for Japanese Text Layout}. 
\url{http://www.w3.org/TR/jlreq/}
\end{thebibliography}

\end{document}