Bottom margin vs. descenders question

[Philip Taylor]

Peter Flynn wrote:

> I had to do it for display math once, so I invented an environment 
> which set the equation, measured it, and output it vertically-centered 
> in a vbox to an integer number of lines. Not elegant, but it helped.

I think you would agree, Peter, that if one is required to typeset on a 
grid, then TeX's normal line-spacing ("leading") behaviour is useless 
and one has to over-ride it to enforce what Adobe call "exact" line 
spacing (e.g., "exactly 12 pt, come hell or high water, and certainly 
regardless of any ascenders, descenders, or other even more pathological 
anomolies").  And to accomplish that, one has to change some of TeX's 
default values, so (for example) one might write :

> \baselineskip = 12 pt
>
> \lineskip = 0 pt
>
> \lineskiplimit = -\maxdimen
>

With those parameters in effect, I have never found it possible to use a 
\vbox with height an integral multiple of \baselineskip to achieve what 
you were setting out to do, because said \vbox has only one reference 
point.  This is why I formulated and proposed my \leaders solution.  
Could I ask you to post a short fragment of code in which you 
demonstrate how your idea would work, given the line-spacing parameters 
above ?

** Phil.



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