Bottom margin vs. descenders question

[Philip Taylor]

I think, David, that Doug was asking about typographical rules rather 
than TeX practice (for which I will need to consult Hart, Brighurst, /et 
al./ before attempting a proper reply) but I am now wondering whether 
there are pathological cases where a TeX descender might protrude into 
the lower margin.  The case I have in mind is as follows.  The page 
consists of normal text with the sole exception of the penultimate line; 
on that line, descenders are grossly exaggerated. Assuming that 
\lineskip (etc) are set such that the penultimate and the final line 
occupy their normal location in the galley (i.e., are not forced apart 
by the excessive descender depth), might the penultimate line's 
descenders intrude into the lower margin, even though the descenders of 
the final line will not ?  The answer would appear to be "yes" —

> % !TeX Program=XeTeX
>
>
> \parskip = 0 pt
>
> \parindent = 0 pt
>
> \obeylines
>
>
> \font \gfont = cmr10 scaled 5000
>
> \def \good {\lower 3,5 ex \hbox {\gfont g}ood }
>
> \lineskip = 0 pt
>
> \lineskiplimit = -\maxdimen
>
>
> \topglue 0 pt
>
> \vfill
>
> The Leith police dismisseth us, for we sufficeth them.
>
> The quick brown fox jumps right over the lazy dog's back.
>
> Now is the time for all \good men to come to the aid of the party.
>
> Here endeth the first lesson.
>
> \eject
>
>
> \end
>

Philip Taylor
--------
David Carlisle wrote:
> tex has a parameter \maxdepth (for the main page) (and \boxmaxdepth 
> for other boxes being constructed) that sets how far you are allowed 
> to go below. If the descenders on the last row are bigger than 
> \maxdepth then the row doesn't fit and the page breaks earlier (or 
> shrinks more or whatever) latex and plain set \maxdepth to 4pt by 
> default so normal letter descenders don't affect the position of the 
> last row.
>
> David
>
> On Thu, 25 Jun 2020 at 05:24, Doug McKenna <doug at mathemaesthetics.com 
> <mailto:doug at mathemaesthetics.com>> wrote:
>
>     Dear typesetting cogniscenti,
>
>     In "official typesetting rules" (TeX or otherwise) are descenders
>     supposed to be completely above the bottom margin bounds of a
>     page?  Or is just the baseline of the bottom line of a full page
>     supposed to conform to the margin bounds?
>
>     Doug McKenna
>     Mathemaesthetics, Inc.
>

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