第一个问题
为什么 unhboxing 似乎忽略了垂直模式，为什么 unvboxing 似乎忽略了水平模式？
接下来两张照片中的 MWE
- 都提供了第一个问题的文本
- 并说明了垂直模式下
\unhbox/和水平模式下/的效果。\unhcopy\unvbox\unvcopy
第一个问题的文本也在下面两张图片中。它们是编译 MWE 的结果。
\newbox\MyBox
\setbox\MyBox=\hbox{%
\vbox{\hbox{box1a}\hbox{box1b}}%
\vbox{\hbox{box2a}\hbox{box2b}}%
\vbox{\hbox{box3a}\hbox{box3b}}%
}
\noindent{%
\bf The {\tt\string\hbox} in box-register {\tt\string\MyBox} is:\hfill\break
\tt\string\hbox\string{\char37 \hfill\break
\null\ \ \ \ \ \ \ %
\string\vbox\string{\string\hbox\string{box1a\string}\string\hbox\string{box1b\string}\string}\char37 \hfill\break
\null\ \ \ \ \ \ \ %
\string\vbox\string{\string\hbox\string{box2a\string}\string\hbox\string{box2b\string}\string}\char37 \hfill\break
\null\ \ \ \ \ \ \ %
\string\vbox\string{\string\hbox\string{box3a\string}\string\hbox\string{box3b\string}\string}\char37 \hfill\break
\null\ \ \ \ \ %
\string}\char37 \hfill
}%
\noindent{\bf In vertical mode I expect boxes to be placed atop/below each
other no matter if the boxes to be placed themselves are horizontal or vertical
boxes.\hfill\break
Thus in vertical mode I expect from {\tt\string\unhcopy}ing the {\tt\string\hbox} held in
box-register {\tt\string\MyBbox} that the three {\tt\string\vbox}es it contains are
placed atop/below each other:}\bigskip
\par\vbox{\hbox{box1a}\hbox{box1b}}%
\vbox{\hbox{box2a}\hbox{box2b}}%
\vbox{\hbox{box3a}\hbox{box3b}}%
\bigskip\noindent{\bf But in vertical mode from {\tt\string\unhcopy}ing I
get the three vertical boxes placed to the left/right of each other, with {\tt\string\parindent}-glue
at the left of the leftmost box:}\bigskip
\par\unhcopy\MyBox
\bigskip\noindent{\bf Just as if I did {\tt\string\box} the {\tt\string\hbox}
in horizontal mode:}\bigskip
\par\leavevmode\box\MyBox
\bigskip\noindent{\bf Why? Where am I wrong in my understanding of the workings of {\tt\string\unhbox}/{\tt\string\unhcopy}?}
\vfill\eject
\setbox\MyBox=\vbox{%
\hbox{\vbox{\hbox{box1a}\hbox{box1b}}}%
\hbox{\vbox{\hbox{box2a}\hbox{box2b}}}%
\hbox{\vbox{\hbox{box3a}\hbox{box3b}}}%
}
\bigskip\noindent{\bf
\bf The {\tt\string\vbox} in box-register {\tt\string\MyBox} is:\hfill\break
\tt
\string\vbox\string{\char37 \hfill\break
\null\ \ \ \ \ \ \ \string\hbox\string{\string\vbox\string{\string\hbox\string{box1a\string}%
\string\hbox\string{box1b\string}\string}\string}\char37 \hfill\break
\null\ \ \ \ \ \ \ \string\hbox\string{\string\vbox\string{\string\hbox\string{box2a\string}%
\string\hbox\string{box2b\string}\string}\string}\char37 \hfill\break
\null\ \ \ \ \ \ \ \string\hbox\string{\string\vbox\string{\string\hbox\string{box3a\string}%
\string\hbox\string{box3b\string}\string}\string}\char37 \hfill\break
\null\ \ \ \ \ \string}\char37 \hfill
}%
\noindent{\bf In horizontal mode I expect boxes to be placed left/right to each other no
matter if the boxes to be placed themselves are horizontal or vertical boxes.\hfill\break
Thus in horizontal mode I expect from {\tt\string\unvcopy}ing the {\tt\string\vbox} held in
box-register {\tt\string\MyBbox} that the three {\tt\string\hbox}es it contains are placed
left/right to each other, with {\tt\string\parindent}-glue at the left of the leftmost
{\tt\string\hbox}:}\bigskip
\leavevmode\hbox{\vbox{\hbox{box1a}\hbox{box1b}}}%
\hbox{\vbox{\hbox{box2a}\hbox{box2b}}}%
\hbox{\vbox{\hbox{box3a}\hbox{box3b}}}%
\bigskip\noindent{\bf But in horizontal mode from {\tt\string\unvcopy}ing
I get the three horizontal boxes placed atop/below each other:}\bigskip
\leavevmode\unvcopy\MyBox
\bigskip\noindent{\bf Just as if I did {\tt\string\box} the {\tt\string\vbox} in vertical mode:}\bigskip
\par\box\MyBox
\bigskip\noindent{\bf Why? Where am I wrong in my understanding of the workings of {\tt\string\unvbox}/{\tt\string\unvcopy}?}
\bye
第二个问题：
假设一个盒子寄存器\MyBox包含一个\vbox，它又包含许多行/许多\hboxes等长度的行。
\box该盒子寄存器产生一个垂直框，其单行不会跨页分割：
\newcount\tmpcnt
\newbox\MyBox
\setbox\MyBox=\vbox{%
\tmpcnt=0 %
\loop\advance\tmpcnt by 1 \hbox to 3cm{Line:\hfill\number\tmpcnt.}\ifnum\tmpcnt<100 \repeat
}%
\noindent
\box\MyBox
\bye
当\unvbox输入该框寄存器时，单行将会被拆分到多个页面：
\newcount\tmpcnt
\newbox\MyBox
\setbox\MyBox=\vbox{%
\tmpcnt=0 %
\loop\advance\tmpcnt by 1 \hbox to 3cm{Line:\hfill\number\tmpcnt.}\ifnum\tmpcnt<100 \repeat
}%
\noindent
\nobreak\unvbox\MyBox
\bye
如何才能实现\unvbox这些行不仅会跨页面拆分，而且还会向右对齐？就像你所做的那样：
\newcount\tmpcnt
\tmpcnt=0 %
\noindent
\loop
\advance\tmpcnt by 1 %
\null\hfill\hbox to 3cm{Line:\hfill\number\tmpcnt.}\break
\ifnum\tmpcnt<100 \repeat
\par
\bye
答案1
\unhbox公开水平列表，因此开始新的段落和新的水平列表，就像一封信一样，常见的\leavevmode 就是\def\leavevmode{\unhbox\voidb@x}