I want one particular application to call gnuplot and display a borderless window. I can tell fvwm to do this for gnuplot by setting:
Style "gnuplot" NoTitle, NoHandles, Sticky, WindowListSkip, BorderWidth 0
But this of course does it for gnuplot all the time. Is there a way of telling gnuplot to only do it just this once,by means such as the commandline or X resources?
You're misunderstanding how X11 windows and window managers work. gnuplot_x11, or any X11 application, for that matter, has exactly *no* control of its own over the decorations of its window --- it controls *only* the interior.
Window decorations are entirely up to the window manager controlling the parent window to decide, i.e. usually that of the root window. What you could do is run gnuplot with X Toolkit Options set to generate its window with a different title / class name (-title, -name), and have the window manager configure to treat that differently from the default window style.
Hah. In all the years, I never knew about these two flags. Thanks! Solved all my probs :)