integrating terminal with gui

5.16: adde/gui/integrating terminal with gui:
. the terminal (aka, command line interface(cli))
can be integrated with the gui features
by printing a stream of windows instead of lines .
. the subwindows roll out of view like lines
but you can drag them out of the cli window
and then they stay pinned .
. these windows are titled command`output#nnn .

5.16: adde/gui/numeric presentations:
. the structures have a natural default
graphic representation,
but numbers have some options
if it doesn't show 3  significant digits,
then we move from decimal notation (n.nn)
to engineering version of scientific notation (n.n e n)
(with exponent a multiple of 3 and we show 6..7 digits )
0.00nnn -> n.nnn e -3
0.000nnnn -> 0.nnnn e -3
0.000,00n -> n.nnn e -6
. if users change the default,
we ask if it should be acct-wide,
it works like a calculator
with format options including
fixed, number of frac digits, sci, eng,
or mixed whole + fractions .