[texhax] raiseboxing \hrulefill in multicolumn{}

[Barbara Beeton]

    I've got a large table with a lot of column-spanning (\multicolumn)
    entries. I want to make it clear when a short-ish entry spans several
    columns by ruling a centred horizontal line either side of the centred
    entry.

    The code:

    ... & \multicolumn{4}{c}{\hrulefill Something \hrulefill} & ...

    does this quite well, the only problem is that the rule is sitting on
    the baseline. I'd like the rule to be centred, say at half the
    x-height. The problem is that no amount of \raisebox{}ing seems to help
    here as all the box commands want a definite width, not a rubber one! On
    the other hand, the basic TeX commands don't seem to play nicely with
    rubber lengths.

    I'm using tabularx so I don't know the exact column-widths, and it's
    clear that tex can do the maths, it's just the rule is a few points too
    low.

in plain tex, you can use a rule with a negative depth
to raise it.  for a rule of thickness 1pt, 2.5pt above
the baseline:

    \vrule height 3.5pt depth-2.5pt width.1fil

this is a \vrule because in a table cell, you're in
horizontal mode.  i'm not positive that .1fil will do
what you want in a tabular situation, but it's worth
a try.

the equivalent in latex would be

    \rule[2.5pt]{.1fil}{1pt}

where 2.5pt = "lift" above baseline, 1pt = height of rule
itself, and .1fil = width -- and i really *don't* know
whether "fil" can be used in this situation; you hint
that it may not, but \rule's follow different rules than
boxes.  all else about the latex \rule is covered in the
excellent book by kopka & daly.
							-- bb