# [texhax] help with identifying some macros

Uwe Lück uwe.lueck at web.de
Thu Oct 15 23:36:52 CEST 2009

Hi Paul,

I neither know about lblot' nor see another occurrence of it. The rest is
about Alignment as described in Chapters 12 and 22 of Knuth's TeXbook.
\strut is a kind of invisible generic symbol to provide (if possible) equal
baseline distances when the usual line spacing method has been disabled.
The latter happens (for reasons I have never investigated) with horizontal
alignment (\halign) that your sample shows, i.e., building tables very
close to TeX's primitives. While the hash mark#' refers to macro
parameters otherwise, it refers to the content of a table cell when
algorithm to process table rows is specified in the first "template" row of
an \halign.

For reasons not entirely clear to me up to now, you find \halign always
within in a "vertical box", \vbox, \vtop, or \vcenter. These three
alternatives refer to alignment of "high" boxes relative to each other in a
line, but also influence "line spacing" (a hard matter of the subject
"baseline-to-baseline skips"). \vtop means that the first line is mainly
considered for alignment within a line, the other lines of it are pushed
down. \vbox focuses on the last line instead. \vcenter centers the whole
stack within a line.

LaTeX provides tabular', array', and similar environments to save you
from learning these things ...

... haha, a try at a resume of some very hard things from TeX in a few
minutes, fostered by some beer, hope it helps though ...

Uwe.

At 22:49 15.10.09, P. R. Stanley wrote:
>Hi folks
>\strut, \vtop and lblot. I'd be grateful for a brief description of each,
>more precisely, the general effect on the presentation.
>
>Here's an example of two of them in use taken from The Z Notation: a
>Reference Manual by Michael Spivey.
>
>$birthday$:
>> known = \{\,{\rm John, Mike, Susan}\,\} \\ >\also > birthday = \{\,\vtop{\halign{\strut#\hfil&{}\mapsto{}#\hfil\cr > John& 25--Mar,\cr > Mike& 20--Dec,\cr > Susan& 20--Dec\,\}.\cr}} >
>Truth be told I've seldom come across anything so cryptic. For example,
>what does the "#" signify?
>Any help would be most appreciated.