It is pretty standard. See e.g. the PostScript Language
> Reference Manual. And, how else to set a solid line with
I didn't know that about postscript. I can easily implement it if it
is "the right thing to do (tm)". But it never occurred to me to
implement a solid line with set_dashes. I would tend to do
Since it is part of postscript, I'll make it the default for mpl too.