[texhax] Alignments and Knuth's uncertainty principle ...

[Philip TAYLOR (Ret'd)]

Oh gurus and TeX-meisters ...

In a horizontal alignment, if (for a given column) no row contains
an entry solely for that column, but instead invariably coalesces
that column either to the left, or to the right, or both, using
\span, how does TeX compute the width of that column.  And, if in
a similar alignment, there are a number of such columns that
abut each other, how does TeX distribute the space amongst them ?

This all comes from trying to typeset family trees, which problem
is driving me quietly insane :-(

** Phil.