The troff collection of tools (including pre- and post-processors) was eventually called Documenter's WorkBench (DWB), and was under continuous development in Bell Labs and later at the spin-off Unix System Laboratories (USL) through 1994. At that time, SoftQuad took over the maintenance, although Brian Kernighan continued to improve troff on his own. Thus, there are at least the following variants of the original Bell Labs troff in use: