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<p class="MsoNormal"><span style="font-family:"Courier New"">Jim Diamond wrote:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> In the context of someone putting some space at the top of the page,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> can anyone explain to me why we care about preserving \prevdepth ?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">When a line of text is placed on a page, TeX tries to place it
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">With its baseline exactly one \baselineskip below the previous<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">line, so TeX inserts enough extra vertical space to achieve that
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">effect.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">This process ignores any vertical space you insert yourself, but
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">does take into account the depth of the previous line (stored in
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\prevdepth). So the amount of extra space added is \baselineskip<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">minus \prevdepth minus the height of the line being added, if
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">that calculated value is positive.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">However, if \prevdepth is equal to exactly -1000pt then the extra
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">space is not added. TeX sets \prevdepth to -1000pt at the start of
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">page and after an \hrule.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Thus,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\hrule height 0pt <o:p>
</o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\vskip -\topskip<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\vskip 5in<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">%\prevdepth now -1000pt<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Text\vfil\eject<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">will place “Text” with the top of the “T” at exactly 5 inches
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">below \voffset.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">But<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\null % place an empty line<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\vskip-\topskip <o:p>
</o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">\vskip 5in<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">%\prevdepth now 0pt<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Text\vfil\eject<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">will place “Text” slightly lower (by the amount \baselineskip
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">minus the height of the “T”).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">HTH<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Daniel H. Luecking<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">University of Arkansas<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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