🚀 go-pugleaf

The one-and-only official DWB pic accepts line by A,B
just fine. It means "relative direction"; e.g.
	line by 1,1 by 1,-1
means "draw a line at 45 degrees from the current
position, then -45 degrees, each segment being the
default line length."
The documentation is exceedingly circumspect on the
semantics of "line by" so I will guess that you have
a reverse engineered version of pic (eg from groff)
and the person doing the reverse engineering couldn't
figure out what it meant.
My conclusion is that the more inscrutable our
documentation, the more difficult our code is to
clone. I'll try to keep that in mind.:-)