# How to use \abovetopsep (to add space between a table's caption and tabular part)?

I read in the documentation of the booktabs package that \abovetopsep can be used to add some space between a table and its caption (instead of the lower-level \vspace{}). However, the exact placement of that option is not clear (at least to me). Is it standalone? Is it an attribute of toprule?

After a few attempts, all failing with "Missing number, treated as zero" it's clear I don't know where to put it. I'm not going to list them as they are obviously incorrect.

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\abovetopsep is a length macro. Use \setlength to modify it, place that in your preamble. For example:
\setlength{\abovetopsep}{1ex}

This space would be added above the line made with \toprule. If you specify the length in your preamble, no change within a table environment is required. Jut put the caption above, the space by \abovetopsep will follow automatically, then comes the toprule. A \midrule, also if placed at the top, would ignore this space.
Isn't \setlength just a macro wrapper for assignment syntax? I.e. isn't \setlength{\abovetopsep}{1ex} equal, in behaviour, to \abovetopsep=1ex ? – Giel Aug 7 '10 at 19:20
@Giel: that's true. \setlength is simply defined: \def\setlength#1#2{#1#2\relax}. The questioner was probably not aware how to use it as a length in general. – Stefan Kottwitz Aug 7 '10 at 19:44