[texhax] \mark causing a blank line

[Stan]

On Sun, 21 Jun 2015 18:22:14 -0500, Donald Arseneau <asnd at triumf.ca> wrote:

> On Sat, June 20, 2015 3:45 pm, Stan wrote:
>
>> This sentence's length and the use of a mark create an unexpected blank
>> line below for some reason..... \mark{mark}
>>
>> Removing one period after ``reason'', or the space before the mark,  
>> makes
>> the blank line disappear. (I'm not saying that putting a space there  
>> makes
>> sense.) Does anyone know why this happens? My only guess is that the  
>> mark
>> prevents the space before it from being removed when TeX breaks the text
>> into lines. I'm not sure if this is a bug, but it seems odd, at least.
>
> Not at all odd.  There is a line-break before the \mark and the
> \mark appears on a line by itself.  The same would happen for \hbox{}
> or \vadjust{}.  (In fact, \mark works quite a bit like \vadjust in that
> it migrates to the vertical list.)

There's a big difference to me between what happens with \hbox{} and what  
happens with \vadjust, since \hbox{} creates something (sure, it's an  
empty thing, but still a thing) that gets put in the horizontal list and  
is meant to stay there. Is there a reason to treat things that migrate to  
the vertical list in the same way in this context? (Not trying to sound  
antagonistic. Just curious.)


Stan