I almost agree with Ingo. A blank line in tbl is generally equivalent to
a table line in which all fields are empty. It is also generally equivalent
to .sp 1. These interpretations differ in the presence of .blm or .ns.
By decorating every table line with an initial \&, tbl has picked the
former in
[lots of context preserved here; sorry for the deep quoting]
At 2020-01-23T04:33:27+0100, Ingo Schwarze wrote:
> >> 1. In man/groff_char.7.man, the blank lines were inside tbl(1)
> >> code. In that context, the meaning of a blank line is well
> >> defined: it means a table row without any cells,
