Compare this
\nonstopmode
\tracingonline=1
\showboxdepth=\maxdimen
\showboxbreadth=\maxdimen
\output={\shipout\vbox{
\unvbox255
\showlists
}}
\nopagenumbers
\noindent A
\bye
and this
\nonstopmode
\tracingonline=1
\showboxdepth=\maxdimen
\showboxbreadth=\maxdimen
\newbox\pagebox
\let\oldshipout\shipout
\def\shipout{\global\let\shipout\oldshipout\afterassignment\myboat\setbox\pagebox=}
\def\myboat{\aftergroup\myship}
\def\myship{\setbox\pagebox=\vbox{
\unvbox\pagebox
\showlists
}\shipout\box\pagebox}
\nopagenumbers
\noindent A
\bye
In the second trace we have some additional output compared to that of the first example, namely:
- Additional output of the second example before identical output of both examples:
\vbox(0.0+0.0)x469.75499, glue set 14.0fil
.\glue -22.5
.\hbox(8.5+0.0)x469.75499, glue set 469.75499fil
..\vbox(8.5+0.0)x0.0
..\glue 0.0 plus 1.0fil
.\glue 0.0 plus 1.0fil minus 1.0fil
\vbox(643.20255+0.0)x469.75499, glue set 633.20255fill
- Additional output of the second example after identical output of both examples:
\glue(\baselineskip) 24.0
\hbox(0.0+0.0)x469.75499, glue set 469.75499fil
.\glue 0.0 plus 1.0fil
where 643.20255
equals 8.9in (i.e., 11 - 1 - 1 - 0.1
) and 469.75499
equals 6.5in (i.e., 8.5 - 1 - 1
)
The question is about this additional output - what does it mean and why does it appear in the second example?