chapter06.tex

% -*- coding: utf-8 -*-
\documentclass{book}

\input{preamble}
\setcounter{chapter}{5}

\begin{document}

%\chapter{Horizontal and Vertical Mode}\label{hvmode}
%\label{chap:hvmode}
\chapter{Horizontal and Vertical Mode}\label{hvmode}
\label{chap:hvmode}

%At any point in its processing \TeX\ is in some \indexterm{mode}.
%There are six modes, divided in three categories:
%\begin{enumerate}
%\item horizontal mode and restricted horizontal mode,
%\item vertical mode and internal vertical mode, and
%\item math mode and display math mode.
%\end{enumerate}
%The math modes will be treated elsewhere (see page~\pageref{math:modes}).
%Here we shall look
%at the horizontal and vertical modes, the kinds of objects
%that can occur in the corresponding lists, and the
%commands that are exclusive for one mode or the other. 
At any point in its processing \TeX\ is in some \indexterm{mode}.
There are six modes, divided in three categories:
\begin{enumerate}
\item horizontal mode and restricted horizontal mode,
\item vertical mode and internal vertical mode, and
\item math mode and display math mode.
\end{enumerate}
The math modes will be treated elsewhere (see page~\pageref{math:modes}).
Here we shall look
at the horizontal and vertical modes, the kinds of objects
that can occur in the corresponding lists, and the
commands that are exclusive for one mode or the other. 

%\label{cschap:vadjust}\label{cschap:showlists}
%\begin{inventory}
%\item [\cs{ifhmode}] 
%      Test whether the current mode is (possibly restricted) horizontal mode.
\label{cschap:vadjust}\label{cschap:showlists}
\begin{inventory}
\item [\cs{ifhmode}] 
      Test whether the current mode is (possibly restricted) horizontal mode.

%\item [\cs{ifvmode}] 
%      Test whether the current mode is (possibly internal) vertical mode.
\item [\cs{ifvmode}] 
      Test whether the current mode is (possibly internal) vertical mode.

%\item [\cs{ifinner}] 
%      Test whether the current mode is an internal mode.
\item [\cs{ifinner}] 
      Test whether the current mode is an internal mode.

%\item [\cs{vadjust}] 
%      Specify vertical material for the enclosing vertical list
%      while in horizontal mode.
\item [\cs{vadjust}] 
      Specify vertical material for the enclosing vertical list
      while in horizontal mode.

%\item [\cs{showlists}] 
%      Write to the log file the contents of the partial lists 
%      currently being built in all modes.
%\end{inventory}
\item [\cs{showlists}] 
      Write to the log file the contents of the partial lists 
      currently being built in all modes.
\end{inventory}

%%\point Horizontal and vertical mode
%\section{Horizontal and vertical mode}
%\point Horizontal and vertical mode
\section{Horizontal and vertical mode}

%When not typesetting mathematics, \TeX\ is in horizontal
%or vertical mode, building horizontal or vertical lists
%respectively. Horizontal mode is typically used to
%make lines of text; vertical mode is typically used
%to stack the lines of a paragraph on top of each other.
%Note that
%these modes
%are different from the internal states of \TeX's input processor
%(see page~\pageref{input:states}).
When not typesetting mathematics, \TeX\ is in horizontal
or vertical mode, building horizontal or vertical lists
respectively. Horizontal mode is typically used to
make lines of text; vertical mode is typically used
to stack the lines of a paragraph on top of each other.
Note that
these modes
are different from the internal states of \TeX's input processor
(see page~\pageref{input:states}).

%%\spoint Horizontal mode
%\subsection{Horizontal mode}
%\spoint Horizontal mode
\subsection{Horizontal mode}

%The main activity in \indextermbus{horizontal}{mode} is building lines of text.
%Text on the page and text in a \cs{vbox} or \cs{vtop} is built in
%horizontal mode (this might be called `paragraph mode');
%if the text is in an \cs{hbox} there is only one line
%of text, and the corresponding mode is the restricted
%horizontal mode.
The main activity in \indextermbus{horizontal}{mode} is building lines of text.
Text on the page and text in a \cs{vbox} or \cs{vtop} is built in
horizontal mode (this might be called `paragraph mode');
if the text is in an \cs{hbox} there is only one line
of text, and the corresponding mode is the restricted
horizontal mode.

%In horizontal mode all material is added to a horizontal list.
%If this list is built in unrestricted horizontal mode, it
%will later be broken into lines and added to the surrounding vertical list.
In horizontal mode all material is added to a horizontal list.
If this list is built in unrestricted horizontal mode, it
will later be broken into lines and added to the surrounding vertical list.

%Each element of a \indextermbus{horizontal}{list} is one of the following:
%\begin{itemize} \item a box (a character, ligature, \cs{vrule},
%or a \gr{box}),
%\item a discretionary break,
%\item a whatsit (see Chapter~\ref{io}),
%\item vertical material enclosed in \cs{mark},
%\cs{vadjust}, or \cs{insert},
%\item 
%\mdqon
%glue or leaders, a kern, a penalty, or a math-on/""off item.
%\mdqoff
%\end{itemize}
%The items in the last point are all discardable.
%\emph{Discardable items}\index{discardable items}
%are called that, because they disappear in
%a break. Breaking of horizontal
%lists is discussed in Chapter~\ref{line:break}.
Each element of a \indextermbus{horizontal}{list} is one of the following:
\begin{itemize} \item a box (a character, ligature, \cs{vrule},
or a \gr{box}),
\item a discretionary break,
\item a whatsit (see Chapter~\ref{io}),
\item vertical material enclosed in \cs{mark},
\cs{vadjust}, or \cs{insert},
\item 
\mdqon
glue or leaders, a kern, a penalty, or a math-on/""off item.
\mdqoff
\end{itemize}
The items in the last point are all discardable.
\emph{Discardable items}\index{discardable items}
are called that, because they disappear in
a break. Breaking of horizontal
lists is discussed in Chapter~\ref{line:break}.

%\subsection{Vertical mode}
\subsection{Vertical mode}

%\emph{Vertical mode}\index{mode!vertical}
%can be used to stack items on top of one another.
%Most of the time, these items are boxes 
%containing the lines of paragraphs.
\emph{Vertical mode}\index{mode!vertical}
can be used to stack items on top of one another.
Most of the time, these items are boxes 
containing the lines of paragraphs.

%Stacking material can take place inside a 
%vertical box, but the
%items that are stacked can also 
%appear by themselves on the page. In the latter case
%\TeX\ is in vertical mode; in the former case, inside a
%vertical box, \TeX\ operates in internal vertical mode.
Stacking material can take place inside a 
vertical box, but the
items that are stacked can also 
appear by themselves on the page. In the latter case
\TeX\ is in vertical mode; in the former case, inside a
vertical box, \TeX\ operates in internal vertical mode.

%In vertical mode all material is added to a vertical list.
%If this list is built in external vertical mode, it
%will later be broken when pages are formed.
In vertical mode all material is added to a vertical list.
If this list is built in external vertical mode, it
will later be broken when pages are formed.

%Each element of a \indextermbus{vertical}{list} is one of the following:
%\begin{itemize}
%\item a box (a horizontal or vertical box or an \cs{hrule}),
%\item a whatsit,
%\item a mark,
%\item glue or leaders, a kern, or a penalty.
%\end{itemize}
%The items in the last point are all discardable.
%Breaking of vertical lists
%is discussed in Chapter~\ref{page:break}.
Each element of a \indextermbus{vertical}{list} is one of the following:
\begin{itemize}
\item a box (a horizontal or vertical box or an \cs{hrule}),
\item a whatsit,
\item a mark,
\item glue or leaders, a kern, or a penalty.
\end{itemize}
The items in the last point are all discardable.
Breaking of vertical lists
is discussed in Chapter~\ref{page:break}.

%There are a few exceptional conditions at the beginning
%of  a vertical list: the value of \cs{prevdepth} is set
%to \n{-1000pt}. Furthermore, no \cs{parskip} glue is added
%at the top of an internal vertical list; 
%at the top of the main vertical list (the top of the
%`current page') no glue or other discardable items
%are added, and \cs{topskip} glue is added when the
%first box is placed on this list
%(see Chapters \ref{page:shape} and~\ref{page:break}).
There are a few exceptional conditions at the beginning
of  a vertical list: the value of \cs{prevdepth} is set
to \n{-1000pt}. Furthermore, no \cs{parskip} glue is added
at the top of an internal vertical list; 
at the top of the main vertical list (the top of the
`current page') no glue or other discardable items
are added, and \cs{topskip} glue is added when the
first box is placed on this list
(see Chapters \ref{page:shape} and~\ref{page:break}).

%%\point Horizontal and vertical commands
%\section{Horizontal and vertical commands}
%\point Horizontal and vertical commands
\section{Horizontal and vertical commands}

%Some commands are so intrinsically horizontal or vertical
%in nature that they force \TeX\ to go into that mode, if
%possible. A~command that forces \TeX\ into horizontal mode
%is called a \gr{horizontal command}; similarly a command that
%forces \TeX\ into vertical mode is called a
%\gr{vertical command}.
Some commands are so intrinsically horizontal or vertical
in nature that they force \TeX\ to go into that mode, if
possible. A~command that forces \TeX\ into horizontal mode
is called a \gr{horizontal command}; similarly a command that
forces \TeX\ into vertical mode is called a
\gr{vertical command}.

%However, not all transitions are possible:
%\TeX\ can switch from both vertical modes to 
%(unrestricted) horizontal mode and back
%through horizontal and vertical commands, but no transitions
%to or from restricted horizontal mode are possible
%(other than by enclosing horizontal boxes in vertical boxes or
%the other way around).
%A~vertical command in restricted horizontal mode thus gives
%an error; the \cs{par} command in restricted horizontal mode
%has no effect.
However, not all transitions are possible:
\TeX\ can switch from both vertical modes to 
(unrestricted) horizontal mode and back
through horizontal and vertical commands, but no transitions
to or from restricted horizontal mode are possible
(other than by enclosing horizontal boxes in vertical boxes or
the other way around).
A~vertical command in restricted horizontal mode thus gives
an error; the \cs{par} command in restricted horizontal mode
has no effect.

%The \indextermbus{horizontal}{commands} are the following:
%\label{h:com:list}
%\begin{itemize}
%\item any \gr{letter}, \gr{otherchar}, \cs{char}, 
%a control sequence defined by \cs{chardef}, or \cs{noboundary};
%\item \cs{accent}, \cs{discretionary}, the discretionary
%hyphen~\verb|\-| and control space~\verb|\|\n{\char32};
%\item \cs{unhbox} and \cs{unhcopy};
%\item \cs{vrule} and the
%\gr{horizontal skip} commands
%\cs{hskip}, \cs{hfil}, \cs{hfill}, \cs{hss}, and \cs{hfilneg};
%\item \cs{valign};
%\item math shift (\n\$).
%\end{itemize}
The \indextermbus{horizontal}{commands} are the following:
\label{h:com:list}
\begin{itemize}
\item any \gr{letter}, \gr{otherchar}, \cs{char}, 
a control sequence defined by \cs{chardef}, or \cs{noboundary};
\item \cs{accent}, \cs{discretionary}, the discretionary
hyphen~\verb|\-| and control space~\verb|\|\n{\char32};
\item \cs{unhbox} and \cs{unhcopy};
\item \cs{vrule} and the
\gr{horizontal skip} commands
\cs{hskip}, \cs{hfil}, \cs{hfill}, \cs{hss}, and \cs{hfilneg};
\item \cs{valign};
\item math shift (\n\$).
\end{itemize}

%The \indextermbus{vertical}{commands} are the following:
%\label{v:com:list}
%\begin{itemize}
%\item \cs{unvbox} and \cs{unvcopy};
%\item \cs{hrule} and the \gr{vertical skip} commands
% \cs{vskip}, \cs{vfil}, \cs{vfill}, \cs{vss}, and \cs{vfilneg};
%\item \cs{halign};
%\item \cs{end} and \cs{dump}.
%\end{itemize}
%Note that the vertical commands do not include \cs{par};
%nor are \cs{indent} and \cs{noindent} horizontal commands.
The \indextermbus{vertical}{commands} are the following:
\label{v:com:list}
\begin{itemize}
\item \cs{unvbox} and \cs{unvcopy};
\item \cs{hrule} and the \gr{vertical skip} commands
 \cs{vskip}, \cs{vfil}, \cs{vfill}, \cs{vss}, and \cs{vfilneg};
\item \cs{halign};
\item \cs{end} and \cs{dump}.
\end{itemize}
Note that the vertical commands do not include \cs{par};
nor are \cs{indent} and \cs{noindent} horizontal commands.

%The connection between boxes and modes is explored below;
%see Chapter~\ref{rules} for more on the connection between
%rules and modes.
The connection between boxes and modes is explored below;
see Chapter~\ref{rules} for more on the connection between
rules and modes.

%\section{The internal modes}
\section{The internal modes}

%The \indextermbus{restricted horizontal}{mode} and 
%\indextermbus{internal vertical}{mode}
%are those variants of horizontal mode and vertical mode
%that hold inside an \cs{hbox} and \cs{vbox} (or \cs{vtop}
%or \cs{vcenter}) respectively.
%However, restricted horizontal mode is rather more
%restricted in nature than internal vertical mode.
%The third internal mode is non-display math mode
%(see Chapter~\ref{math}).
The \indextermbus{restricted horizontal}{mode} and 
\indextermbus{internal vertical}{mode}
are those variants of horizontal mode and vertical mode
that hold inside an \cs{hbox} and \cs{vbox} (or \cs{vtop}
or \cs{vcenter}) respectively.
However, restricted horizontal mode is rather more
restricted in nature than internal vertical mode.
The third internal mode is non-display math mode
(see Chapter~\ref{math}).

%%\spoint Restricted horizontal mode
%\subsection{Restricted horizontal mode}
%\spoint Restricted horizontal mode
\subsection{Restricted horizontal mode}

%The main difference between restricted horizontal mode,
%the mode in an \cs{hbox}, and unrestricted horizontal mode,
%the mode in which paragraphs in vertical boxes
%and on the page are built,
%is that you cannot break out of restricted horizontal mode: 
%\cs{par}~does nothing in this mode. 
%Furthermore, a~\gram{vertical command} in restricted horizontal
%mode gives an error. 
%In unrestricted horizontal mode it would cause a
%\cs{par} token to be inserted and vertical mode to be entered
%(see also Chapter~\ref{par:end}).
The main difference between restricted horizontal mode,
the mode in an \cs{hbox}, and unrestricted horizontal mode,
the mode in which paragraphs in vertical boxes
and on the page are built,
is that you cannot break out of restricted horizontal mode: 
\cs{par}~does nothing in this mode. 
Furthermore, a~\gram{vertical command} in restricted horizontal
mode gives an error. 
In unrestricted horizontal mode it would cause a
\cs{par} token to be inserted and vertical mode to be entered
(see also Chapter~\ref{par:end}).

%%\spoint Internal vertical mode
%\subsection{Internal vertical mode}
%\spoint Internal vertical mode
\subsection{Internal vertical mode}

%Internal vertical mode, the vertical mode inside
%a~\cs{vbox}, is a lot like external vertical
%mode, the mode in which pages are built.
%A~\gram{horizontal command} in internal vertical mode,
%for instance, is perfectly valid:
%\TeX\ then starts building a paragraph in
%unrestricted horizontal mode.
Internal vertical mode, the vertical mode inside
a~\cs{vbox}, is a lot like external vertical
mode, the mode in which pages are built.
A~\gram{horizontal command} in internal vertical mode,
for instance, is perfectly valid:
\TeX\ then starts building a paragraph in
unrestricted horizontal mode.

%One difference is that the commands
%\cs{unskip} and \cs{unkern} have no effect
%in external vertical mode, and
%\cs{lastbox} is always empty in external vertical mode.
%See further pages \pageref{lastbox} and~\pageref{unskip}.
One difference is that the commands
\cs{unskip} and \cs{unkern} have no effect
in external vertical mode, and
\cs{lastbox} is always empty in external vertical mode.
See further pages \pageref{lastbox} and~\pageref{unskip}.

%The entries of alignments (see Chapter~\ref{align}) are 
%processed in internal modes: restricted horizontal mode
%for the entries of an \cs{halign}, and internal vertical
%mode for the entries of a~\cs{valign}.
%The material in \cs{vadjust}   and \cs{insert} items
%is also processed in internal vertical mode; furthermore,
%\TeX\ enters this mode when processing the \cs{output} token list.
The entries of alignments (see Chapter~\ref{align}) are 
processed in internal modes: restricted horizontal mode
for the entries of an \cs{halign}, and internal vertical
mode for the entries of a~\cs{valign}.
The material in \cs{vadjust}   and \cs{insert} items
is also processed in internal vertical mode; furthermore,
\TeX\ enters this mode when processing the \cs{output} token list.

%The commands \cs{end} and \cs{dump} (the latter exists only in \IniTeX)
%are not allowed in
%internal vertical mode; furthermore, \cs{dump} is not allowed
%inside a group (see Chapter~\ref{TeXcomm}).
The commands \cs{end} and \cs{dump} (the latter exists only in \IniTeX)
are not allowed in
internal vertical mode; furthermore, \cs{dump} is not allowed
inside a group (see Chapter~\ref{TeXcomm}).


%%\point[hvbox]  Boxes and modes
%\section{Boxes and modes}
%\label{hvbox}
%\point[hvbox]  Boxes and modes
\section{Boxes and modes}
\label{hvbox}

%There are horizontal and vertical boxes, and there is
%horizontal and vertical mode. Not surprisingly, there is
%a connection between the boxes and the modes.
%One can ask about this connection in two ways.
There are horizontal and vertical boxes, and there is
horizontal and vertical mode. Not surprisingly, there is
a connection between the boxes and the modes.
One can ask about this connection in two ways.

%%\spoint What box do you use in what mode?
%\subsection{What box do you use in what mode?}
%\spoint What box do you use in what mode?
\subsection{What box do you use in what mode?}

%This is the wrong question. Both horizontal  and vertical boxes
%can be used in both horizontal and vertical mode. 
%Their placement is determined by the prevailing mode at that moment.
This is the wrong question. Both horizontal  and vertical boxes
can be used in both horizontal and vertical mode. 
Their placement is determined by the prevailing mode at that moment.

%%\spoint What mode holds in what box?
%\subsection{What mode holds in what box?}
%\spoint What mode holds in what box?
\subsection{What mode holds in what box?}

%This is the right question.
%When an \cs{hbox} starts, \TeX\ is in restricted horizontal
%mode. Thus everything in a horizontal box is lined up horizontally.
This is the right question.
When an \cs{hbox} starts, \TeX\ is in restricted horizontal
mode. Thus everything in a horizontal box is lined up horizontally.

%When a \cs{vbox} is started, \TeX\ is in internal vertical mode.
%Boxes of both kinds and other items are then stacked
%on top of each other.
When a \cs{vbox} is started, \TeX\ is in internal vertical mode.
Boxes of both kinds and other items are then stacked
on top of each other.


%%\spoint Mode-dependent behaviour of boxes
%\subsection{Mode-dependent behaviour of boxes}
%\spoint Mode-dependent behaviour of boxes
\subsection{Mode-dependent behaviour of boxes}

%Any \gr{box} (see Chapter \ref{boxes} for the full definition)
%can be used in horizontal, vertical, and math mode.
%Unboxing commands, however, are specific for horizontal or vertical mode.
%Both \cs{unhbox} and \cs{unhcopy} are \gr{horizontal command}s,
%so they can make \TeX\ switch from vertical to horizontal
%mode; 
%both \cs{unvbox} and \cs{unvcopy} are \gr{vertical command}s,
%so they can make \TeX\ switch from horizontal to vertical
%mode.
Any \gr{box} (see Chapter \ref{boxes} for the full definition)
can be used in horizontal, vertical, and math mode.
Unboxing commands, however, are specific for horizontal or vertical mode.
Both \cs{unhbox} and \cs{unhcopy} are \gr{horizontal command}s,
so they can make \TeX\ switch from vertical to horizontal
mode; 
both \cs{unvbox} and \cs{unvcopy} are \gr{vertical command}s,
so they can make \TeX\ switch from horizontal to vertical
mode.

%In horizontal mode the \cs{spacefactor} is set to 1000
%after a box has been placed. In vertical mode the
%\cs{prevdepth} is set to the depth of the box placed.
%Neither statement holds for
%unboxing commands: after an \cs{unhbox} or \cs{unhcopy} the 
%spacefactor is not altered, and after \cs{unvbox} or \cs{unvcopy}
%the \cs{prevdepth} remains unchanged.
%After all, these commands do not add a box,
%but a piece of a~(horizontal or vertical) list.
In horizontal mode the \cs{spacefactor} is set to 1000
after a box has been placed. In vertical mode the
\cs{prevdepth} is set to the depth of the box placed.
Neither statement holds for
unboxing commands: after an \cs{unhbox} or \cs{unhcopy} the 
spacefactor is not altered, and after \cs{unvbox} or \cs{unvcopy}
the \cs{prevdepth} remains unchanged.
After all, these commands do not add a box,
but a piece of a~(horizontal or vertical) list.

%The operations \cs{raise} and \cs{lower} can only be
%applied to a box in horizontal mode; similarly, \cs{moveleft} and
%\cs{moveright} can only be applied in vertical mode.
The operations \cs{raise} and \cs{lower} can only be
applied to a box in horizontal mode; similarly, \cs{moveleft} and
\cs{moveright} can only be applied in vertical mode.


%%\point Modes and glue
%\section{Modes and glue}
%\point Modes and glue
\section{Modes and glue}

%Both in horizontal and vertical mode
%\TeX\ can insert glue items the size of which is
%determined by the preceding object in the list.
Both in horizontal and vertical mode
\TeX\ can insert glue items the size of which is
determined by the preceding object in the list.

%For horizontal mode the amount of glue that is inserted
%for a space token depends on the \cs{spacefactor} of
%the previous object in the list. This is treated
%in Chapter~\ref{space}.
For horizontal mode the amount of glue that is inserted
for a space token depends on the \cs{spacefactor} of
the previous object in the list. This is treated
in Chapter~\ref{space}.

%In vertical mode \TeX\ inserts glue to keep boxes at a certain
%distance from each other. This glue is influenced by the
%height of the current item and the depth of the previous one.
%The depth of items is recorded in the \cs{prevdepth} parameter
%(see Chapter~\ref{baseline}).
In vertical mode \TeX\ inserts glue to keep boxes at a certain
distance from each other. This glue is influenced by the
height of the current item and the depth of the previous one.
The depth of items is recorded in the \cs{prevdepth} parameter
(see Chapter~\ref{baseline}).

%The two quantities \cs{prevdepth} 
%and \cs{spacefactor} 
%use the same internal register of \TeX. Thus the \cs{prevdepth}
%can be used or asked only in vertical mode, and the \cs{spacefactor}
%only in horizontal mode.
The two quantities \cs{prevdepth} 
and \cs{spacefactor} 
use the same internal register of \TeX. Thus the \cs{prevdepth}
can be used or asked only in vertical mode, and the \cs{spacefactor}
only in horizontal mode.

%%\point[migrate] Migrating material
%\section{Migrating material}
%\label{migrate}
%\point[migrate] Migrating material
\section{Migrating material}
\label{migrate}

%The three control sequences \cs{insert}, \cs{mark}, and \cs{vadjust}
%can be given in a paragraph 
%(the first two can also occur
%in vertical mode) to specify \indexterm{migrating material}:
%material that will wind up on the
%surrounding vertical list rather than on the current list.
%Note that this need not be 
%the main vertical list: it can be a vertical box
%containing a paragraph of text. In this case a \cs{mark}
%or \cs{insert} command will not reach the page breaking algorithm.
The three control sequences \cs{insert}, \cs{mark}, and \cs{vadjust}
can be given in a paragraph 
(the first two can also occur
in vertical mode) to specify \indexterm{migrating material}:
material that will wind up on the
surrounding vertical list rather than on the current list.
Note that this need not be 
the main vertical list: it can be a vertical box
containing a paragraph of text. In this case a \cs{mark}
or \cs{insert} command will not reach the page breaking algorithm.

%When several migrating items are specified in a certain line
%of text, their left-to-right order is preserved when they are
%placed on the surrounding vertical list. These items are placed
%directly after the horizontal box containing the line of text
%in which they were specified: they come before any
%penalty or glue items that are automatically inserted
%(see page~\pageref{between:lines}).
When several migrating items are specified in a certain line
of text, their left-to-right order is preserved when they are
placed on the surrounding vertical list. These items are placed
directly after the horizontal box containing the line of text
in which they were specified: they come before any
penalty or glue items that are automatically inserted
(see page~\pageref{between:lines}).

%%\spoint \cs{vadjust}
%\subsection{\cs{vadjust}}
%\spoint \cs{vadjust}
\subsection{\cs{vadjust}}

%The command
%\cstoidx vadjust\par
%\begin{disp}\cs{vadjust}\gr{filler}\lb\gr{vertical mode material}\rb\end{disp}
%is only allowed in horizontal and math modes (but it is
%not a \gr{horizontal command}).
%Vertical mode material specified by \cs{vadjust} is moved from
%the horizontal list in which the command is given
%to the surrounding vertical list, directly after the box
%in which it occurred.
The command
\cstoidx vadjust\par
\begin{disp}\cs{vadjust}\gr{filler}\lb\gr{vertical mode material}\rb\end{disp}
is only allowed in horizontal and math modes (but it is
not a \gr{horizontal command}).
Vertical mode material specified by \cs{vadjust} is moved from
the horizontal list in which the command is given
to the surrounding vertical list, directly after the box
in which it occurred.

%In the current line
%\vadjust{\setbox0=\hbox{$\bullet$\hskip1em}\ht0=0pt \dp0=0pt \llap{\box0}}
%a \cs{vadjust} item was placed to put the bullet in the margin.
In the current line
\vadjust{\setbox0=\hbox{$\bullet$\hskip1em}\ht0=0pt \dp0=0pt \llap{\box0}}
a \cs{vadjust} item was placed to put the bullet in the margin.


%Any vertical material in a \cs{vadjust} item is processed
%in internal vertical mode, even though it will wind up
%on the main vertical list. For instance, the \cs{ifinner}
%test is true in a \cs{vadjust}, and at the start
%\mdqon
%of the vertical material \cs{prevdepth}$=$""\n{-1000pt}.
%\mdqoff
Any vertical material in a \cs{vadjust} item is processed
in internal vertical mode, even though it will wind up
on the main vertical list. For instance, the \cs{ifinner}
test is true in a \cs{vadjust}, and at the start
\mdqon
of the vertical material \cs{prevdepth}$=$""\n{-1000pt}.
\mdqoff

%%\point Testing modes
%\section{Testing modes}
%\point Testing modes
\section{Testing modes}

%The three conditionals \cs{ifhmode}, \cs{ifvmode}, and
%\cs{ifinner} can distinguish between the four modes of
%\TeX\ that are not math modes.
%The \cs{ifinner} test is true if \TeX\ is in 
%restricted horizontal mode or internal vertical mode
%(or in non-display math mode).
%Exceptional condition: during a \cs{write} \TeX\
%is in a `no mode' state. The tests \cs{ifhmode},
%\cs{ifvmode}, and \cs{ifmmode} are then all false.
The three conditionals \cs{ifhmode}, \cs{ifvmode}, and
\cs{ifinner} can distinguish between the four modes of
\TeX\ that are not math modes.
The \cs{ifinner} test is true if \TeX\ is in 
restricted horizontal mode or internal vertical mode
(or in non-display math mode).
Exceptional condition: during a \cs{write} \TeX\
is in a `no mode' state. The tests \cs{ifhmode},
\cs{ifvmode}, and \cs{ifmmode} are then all false.

%Inspection of all current lists, including the `recent
%contributions' (see Chapter~\ref{page:break}),
%is possible through the command \csidx{showlists}\label{showlists}.
%This command writes to the log file the contents of all
%lists that are being built at the moment the command is given.
Inspection of all current lists, including the `recent
contributions' (see Chapter~\ref{page:break}),
is possible through the command \csidx{showlists}\label{showlists}.
This command writes to the log file the contents of all
lists that are being built at the moment the command is given.

%Consider the example
%\begin{verbatim}
%a\hfil\break b\par 
%c\hfill\break d
%\hbox{e\vbox{f\showlists
%\end{verbatim}
%Here the first paragraph has been broken into two lines, and
%these have been added to the current page. The second paragraph
%has not been concluded or broken into lines.
Consider the example
\begin{verbatim}
a\hfil\break b\par 
c\hfill\break d
\hbox{e\vbox{f\showlists
\end{verbatim}
Here the first paragraph has been broken into two lines, and
these have been added to the current page. The second paragraph
has not been concluded or broken into lines.

%The log file shows the following. \TeX\ was busy
%building a paragraph (starting with an indentation box
%\n{20pt} wide):\begin{verbatim}
%### horizontal mode entered at line 3
%\hbox(0.0+0.0)x20.0
%\tenrm f
%spacefactor 1000
%\end{verbatim}
%This paragraph was inside a vertical box:\begin{verbatim}
%### internal vertical mode entered at line 3
%prevdepth ignored
%\end{verbatim}
%The vertical box was in  a horizontal box, 
%\begin{verbatim}
%### restricted horizontal mode entered at line 3
%\tenrm e
%spacefactor 1000
%\end{verbatim}
%which was part of
%an as-yet unfinished paragraph:\begin{verbatim}
%### horizontal mode entered at line 2
%\hbox(0.0+0.0)x20.0
%\tenrm c
%\glue 0.0 plus 1.0fill
%\penalty -10000
%\tenrm d
%etc.
%spacefactor 1000
%\end{verbatim}
%Note how the infinite glue and the \cs{break} penalty
%are still part of the horizontal list.
The log file shows the following. \TeX\ was busy
building a paragraph (starting with an indentation box
\n{20pt} wide):\begin{verbatim}
### horizontal mode entered at line 3
\hbox(0.0+0.0)x20.0
\tenrm f
spacefactor 1000
\end{verbatim}
This paragraph was inside a vertical box:\begin{verbatim}
### internal vertical mode entered at line 3
prevdepth ignored
\end{verbatim}
The vertical box was in  a horizontal box, 
\begin{verbatim}
### restricted horizontal mode entered at line 3
\tenrm e
spacefactor 1000
\end{verbatim}
which was part of
an as-yet unfinished paragraph:\begin{verbatim}
### horizontal mode entered at line 2
\hbox(0.0+0.0)x20.0
\tenrm c
\glue 0.0 plus 1.0fill
\penalty -10000
\tenrm d
etc.
spacefactor 1000
\end{verbatim}
Note how the infinite glue and the \cs{break} penalty
are still part of the horizontal list.

%Finally, the first paragraph has been broken into lines and 
%added to the current page:\begin{verbatim}
%### vertical mode entered at line 0
%### current page:
%\glue(\topskip) 5.69446
%\hbox(4.30554+0.0)x469.75499, glue set 444.75497fil
%.\hbox(0.0+0.0)x20.0
%.\tenrm a
%.\glue 0.0 plus 1.0fil
%.\penalty -10000
%.\glue(\rightskip) 0.0
%\penalty 300
%\glue(\baselineskip) 5.05556
%\hbox(6.94444+0.0)x469.75499, glue set 464.19943fil
%.\tenrm b
%.\penalty 10000
%.\glue(\parfillskip) 0.0 plus 1.0fil
%.\glue(\rightskip) 0.0
%etc.
%total height 22.0 plus 1.0
% goal height 643.20255
%prevdepth 0.0
%\end{verbatim}
Finally, the first paragraph has been broken into lines and 
added to the current page:\begin{verbatim}
### vertical mode entered at line 0
### current page:
\glue(\topskip) 5.69446
\hbox(4.30554+0.0)x469.75499, glue set 444.75497fil
.\hbox(0.0+0.0)x20.0
.\tenrm a
.\glue 0.0 plus 1.0fil
.\penalty -10000
.\glue(\rightskip) 0.0
\penalty 300
\glue(\baselineskip) 5.05556
\hbox(6.94444+0.0)x469.75499, glue set 464.19943fil
.\tenrm b
.\penalty 10000
.\glue(\parfillskip) 0.0 plus 1.0fil
.\glue(\rightskip) 0.0
etc.
total height 22.0 plus 1.0
 goal height 643.20255
prevdepth 0.0
\end{verbatim}


%\endofchapter
%%%%% end of input file [modes]
\endofchapter
%%%% end of input file [modes]

\end{document}