> > http://troff.org/54.pdf
It is recommended to study this document carefully. groff has useful extensions, but it's best to learn them when you know about the portable subset of the roff language. You e.g. often use requests with register contents as arguments without using a unit. I hope you know what you are doing. It is better to always use a unit in this case (for requests which have default units different from "u").
