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

%%% for LTXexample environment
\usepackage{showexpl,lltjlisting}
\lstset{basicstyle=\ttfamily, width=0.3\textwidth}


\usepackage{mflogo,booktabs}

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%%% Mandatory article metadata %%%
\title{The development of \LuaTeX-ja package}
\author{Hironori Kitagawa}
\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 much 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 codes of \LuaTeX-ja.
}

\newcommand{\parname}[1]{\textsf{#1}}

\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.  There are other methods---for example, using Omega
and OTP~\cite{omegaj}, or with the CJK package---to do so, however,
these alternative methods did not became a majority. On the one hand,
p\TeX\ enables us to produce high-quality documents, but 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 the developments of |ptexenc|~\cite{ptexenc} by Nobuyuki Tsuchimura, 
$\varepsilon$-p\TeX~\cite{eptex} by the author,~and
up\TeX~\cite{uptex} by Takuji Tanaka.

However, there are still lag now. 


Before this \LuaTeX-ja package, there were several attempts to typeset Japanese documents under \LuaTeX.
Here we cite three examples:
\begin{itemize}
\item |luaums.sty|~\cite{luaums} developed by the author. This experimental package is for creating a Japanese-based presentation under \LuaTeX.
\item |luajalayout| package\cite{luajalayout}, formerly known as the |jafontspec| package, by Kazuki Maeda. 
This package is based on \LaTeXe\ and |fontspec| package.
\item |luajp-test| package\cite{luajp-test}, a test package made by Atsuhito Kohda, based on articles on the web page~\cite{joylua}.
\end{itemize}


\subsection{Development Policy of \LuaTeX-ja}
\label{ssec-pol} 
The first aim of the 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 the development proceeds, some
technical/conceptual difficulties are arised. Hence we changed the aim
of the project.
\begin{itemize}
\item\emph{\LuaTeX-ja offers more flexibility of typesetting than that by
     p\TeX.}

     We think that the ability of producing outputs conformed to
     JIS~X~4051~\cite{jisx4051}, the Japanese Industrial Standard for
     typesetting, 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,
which is introduced. Some of them are due to specifications of callbacks
in \LuaTeX\ (\emph{i.e.}, technical reason), and others are which we
thought which are better to be changed, for ``natural''
specifications. In Section~3, we show the current status of the \LuaTeX-ja project.

For implementing features into \LuaTeX-ja, we had to use some tricks in Lua scripts. 
In Section~4, we describe several these tricks and internal processing methods.
We hope that the materials in this section have good applications.


\section{Major differences with \pTeX}
In this section, we breifly look at ** major differences between p\TeX\ and \LuaTeX-ja.
For genral information of Japanese typesetting and the facts about p\TeX, please see Okumara~\cite{ptexjp}.


\subsection{Names of Control Sequences}
\label{ssec-csname}
Since p\TeX\ is a engine modification of Knuth's original \TeX82 engine,
some primitives added in it takes a form that cannot 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 $\langle\hbox{\it
char\_code}\rangle$ 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 for Japanese typesetting which were
mere internal integers, dimensions, or~skips in p\TeX\ that cannot be
implemented by same approaches in \LuaTeX-ja.  These parameters have a
common point; the values at the end of a horizontal box or that of a
paragraph are effective in whole box or paragraph.  A good example of
them is |\kanjiskip|, the default amount of a skip which will be
inserted between two consecutive Japanese characters by default.  The
reason of this is the place of |hpack_filter| in the \LuaTeX's
CWEB-source code, and 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 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{Linebreak after a Japanese Character}
\label{ssec-line} 

Japanese texts can linebreak almost everywhere, in contrast with
alphabetic texts can linebreak only between words (or use
hyphenation). Hence, p\TeX's input processor is modified so that a
linebreak after a Japanese character doesn't emit a space. However,
there is no way to customize the input processor of \LuaTeX, other than
hack its CWEB-source. All we 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 ends with a Japanese
character\footnote{Strictly speaking, it also requires that the catcode
of the endline 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 linebreak by p\TeX\ and that of \LuaTeX-ja is totally same,
but 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; the command at the first
line marks most of Japanese characters as ``non-Japanese character''. In
other words, from this 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 linebreak 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 monospaced,
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, the
difference between |min10.tfm| and |goth10.tfm|, which are JFMs shipped
with p\TeX\ for seriffed \emph{mincho} family and sans-seriffed
\emph{gothic} family, are their |FAMILY| and |FACE| only. Moreover,
|jis.tfm| and |jisg.tfm|, which consists a parts of \emph{jis} font
metric which is used in Haruhiko Okumura's
\emph{jsclasses}~\cite{jsclasses}, are totally same as binary files.
Another example is: if one want to use many fonts which are not
installed in his \TeX\ distribution, of course he needs to prepare TFMs
for them. But, as long as he wants to use Japanese fonts with p\TeX, he
has to only copy and rename some JFM (\emph{e.g.},~copy |jis.tfm| to
|hoge.tfm|).

Considering this situation, we decided to separate ``real'' fonts and
metrics in \LuaTeX-ja, as 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 |luaotfload| package, so
      |file:| prefix and 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, noembedded
      fonts. 
\end{itemize}
We note that |-kern| in features is important, since if kerning information from real font itself will clash with spacing from the metric.

\begin{figure}
\begin{verbatim}
\jfont\foo=file:ipaexm.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}
As described in \cite{luatexref}, \LuaTeX's kerning and ligaturing
process is totally different from that 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 |f{}irm|
(this gives `f\hbox{}irm' in \TeX82). However, \LuaTeX's process is
\emph{node-based}, that is, the process will be done when a horizontal
box of a paragraph is ended, so |f{}irm| and |firm| yield the same
output under \LuaTeX.

The situation for Japanese characters is basically same, but not
entirely.  Glues (and kerns) those will be needed for Japanese
typesetting will be divided into the following three categories:
\begin{description}
\item[Glue (or Kern) from the Metric of Japanese Fonts] 
\item[Default Glue Between a Japanese Character and an Alphabetic Character] 
Usually 1/4 of fullwidth with some stretch and shrink for justifying each line.
\item[Default Glue Between Two Consecutive Japanese Characters] 
The main reason of this glue is to enable line-breaking almost everywhere in Japanese texts. In most cases, its natural width is zero, and
some stretch/shrink for justifying each line. 
\end{description}
In p\TeX, these three kinds of glues are treated differently. The first
 category (\emph{JFM glue}, for short) is inserted when a (sequence of)
 Japanese character is appended to current list, same as alphabetic
 characters in \TeX82. This means that one can interrupt the insertion
 process by saying |{}|.  The second category (\emph{xkanjiskip}, for
 short) is inserted just before `hpack' or line-breaking of a paragraph;
 this timing is somewhat similar to that of \LuaTeX's kerning
 process. The third category (\emph{kanjiskip}, for short) is not
 appeared as a node anywhere; only appears implicitly in calculation of the
 width of a horizontal box or that of linebreaking. 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{figure}
\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}
\caption{Examples of differences between  p\TeX\ and \LuaTeX-ja,}
\label{fig-jfmglue}
\end{figure}

\begin{figure}
\begin{center}
\fontsize{40}{40}\selectfont\fboxsep=0mm
\fbox{\vrule width0pt height\cht depth\cdp あ}%
\fbox{\vrule width0pt height\cht depth\cdp 】\inhibitglue}%
\fbox{\vrule width0pt height\cht depth\cdp\kern.5\zw}%
\fbox{\vrule width0pt height\cht depth\cdp\kern.5\zw}%
\fbox{\vrule width0pt height\cht depth\cdp\hbox{}\inhibitglue【}%
\fbox{\vrule width0pt height\cht depth\cdp 〙\inhibitglue}%
\fbox{\vrule width0pt height\cht depth\cdp\kern.5\zw}%
\fbox{\vrule width0pt height\cht depth\cdp\kern.5\zw}%
\fbox{\vrule width0pt height\cht depth\cdp \hbox{}\inhibitglue〘}%
\end{center}
\caption{Detail of (1) in Figure~\ref{fig-jfmglue}.}
\label{fig-ptexjfm}
\end{figure}

Now we will take a look inside the insertion process itself. 

\begin{description}
\item[Ignored Nodes]
As noted in the previous subsection, the insertion process in p\TeX\ is
           interrupted by saying |{}| or anything else. This leads the
           second row in Figure~\ref{fig-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 nodes will be
           ignored,}\ in \LuaTeX-ja, as shown in (1) in
           Figure~\ref{fig-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 kerns from italic correction for $p$, and
           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, to 

\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 we assume that all Japanese fonts
           use same metric, and |\gt| selects \emph{gothic} 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}
But this is 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}

\end{description}


\section{Current Status of the Development}
At the moment, \LuaTeX-ja can be used under plain \TeX, and under
\LaTeXe. Generally speaking, one has to read |luatexja.sty|, by
|\input| command or |\usepackage|~(\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{\TeX\ engine}. The development of \LuaTeX-ja is started from this
part.  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[Adjusting the baseline of alphabetic characters and/or Japanese characters]

\item[Setting the range of ``Japanese characters''] This feature is
           inspired by up\TeX. up\TeX\ has an additional primitive named
           |\kcatcode| for setting a character is treated as alphabetic
           charaacter, \emph{kana}, \emph{kanji}, \emph{Hangul},
           or~\emph{other CJK character}, and the assignment of
           |\kcatcode| can be done by a block of Unicode\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 in Basic Multilingual Plane which are not included in
           most Japanese fonts, ...
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 consists of the following
           characters:
Considering these two points, ...

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

\subsection{Patches for plain \TeX\ and \LaTeXe}
p\TeX\ has patches 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. We remark two points related to the porting:
\begin{description}
\item[The Default Ranges of Japanese Characters] 


\item[The behavior of\/ {\tt\char92fontfamily\/} command]
The |\fontfamily| command 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 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 make possible this behavior, one has to create a list of already
           defined alphabetic encodings. Hence it works in p\LaTeXe, ...
However, since \LuaTeX-ja is loaded as a package, it will not
           work. 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 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}~\cite{jsclasses} which has developed by Haruhiko
Okumura and now widely used in Japanese \TeX\ users.  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.


\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 select 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), and when current
alphabetic font is changed, the current Japanese font also changes
according to the table.  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 original \TeX. In other words,
these control sequence cannot be an argument of |\the| or |\textfont|, and they are just an assignments to an attribute, in fact.


\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] We described
           this already at Subsection~\ref{ssec-line}. Done in the
           |process_input_buffer| callback.
\item[Font Replacement] In the |hyphenate| callback, we looks into for
           each \textit{glyph\_node}~$p$. If its character is considered
           to be a Japanese character, the font used in $p$ is replaced
           by the value of |\ltj@curjfnt| that is associated
           with~$p$. Also we subtract the subtype of $p$ 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 are main routines of \LuaTeX-ja:

\begin{description}
\item[Examination of Stack Level] We traverse the horizontal list which is the content of a horizontal box 
to determine what is the level of \LuaTeX-ja's internal stack in the end
           of the list. This is needed because of the place of
           |hpack_filter| in the source of \LuaTeX. We will discuss more detail at 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 Places of (Japanese) Characters]
Under \LuaTeX-ja, the size of the virtual body of a Japanese character
           and its position (\emph{i.e.}, offset) are determined by the
           metric, since the optimal width of a character in
           typesetting---in most cases, this is specified width in the
           metric---and the actual width in TrueType/Opentype fonts
           often differ. For example, the width the fullwidth open brace
           `\inhibitglue ｛' is considered to be half-width in
           typesetting, although this character is full-width in
           TrueType fonts like IPA~Mincho.

To adjust size/places of Japanese characters, \LuaTeX-ja encapsules a
           \textit{glyph\_node} which containing a Japanese character
           into a horizontal box which size is specified in the metric.
As the case of `\inhibitglue ｛', a half-widthed horizontal box 
\end{description}

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

As we noted on 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 cannot be implemented by internal integers or
other types. We explain it in this section.



\subsection*{About the Project}
\subsection*{Acknowledgements}


%%% The style of the bibiliogrphy is `amsplain'.
\providecommand{\bysame}{\leavevmode\hbox to3em{\hrulefill}\thinspace}
\providecommand{\href}[2]{#2}
\begin{thebibliography}{9}

%\bibitem{Knuth}
%Donald E.~Knuth, \emph{The \TeX book}, Addison-Wesley, 1986.

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

%\bibitem{Eijkhout}
%Victor Eijkhout, \emph{\TeX\ by Topic, A \TeX nician's Reference}, Addison-Wesley, 1992. \url{http://www.cs.utk.edu/~eijkhout/texbytopic-a4.pdf}

\bibitem{luaums}
Hironori Kitagawa, \textbf{LuaTeXで日本語}\ (in Japanese). \url{http://oku.edu.mie-u.ac.jp/tex/mod/forum/discuss.php?d=378}

\bibitem{luajalayout}
Kazuki Maeda\ (前田一貴), \textbf{luajalayout パッケージ —LuaLaTeX による日本語組版—}\ (in Japanese).
\url{http://www-is.amp.i.kyoto-u.ac.jp/lab/kmaeda/lualatex/luajalayout/}

\bibitem{luajp-test}
Atsuhito Kohda, \textbf{LuaTeXと日本語}\ (in Japanese). \url{http://www1.pm.tokushima-u.ac.jp/~kohda/tex/luatex-old.html}

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

\bibitem{luatexref}
\textbf{The \LuaTeX reference}

\bibitem{jsclasses}
Haruhiko Okumura\ (奥村晴彦), \textbf{pLaTeX2e 新ドキュメントクラス}\ (in Japanese). \url{http://oku.edu.mie-u.ac.jp/~okumura/jsclasses/}

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


\end{thebibliography}

\end{document}