The command \hhline produces a line like \hline, or a double line like \hline\hline, except for its interaction with vertical lines. The command takes a preamble (rather like the preamble of a tabular environment), and this specifies whether there are to be one or two horizontal lines, and what happens when the horizontal line meets a vertical one.

The package is part of the tools bundle in the LaTeX required distribution.

The author is David Carlisle. The package is Copyright © 1991-1994 David Carlisle.