>For the windows created with DEFINE WINDOW, is it possible for a child window to inherit the properties of its container (another window or screen). Because I would like if I change the font of a window to change also the font of its child window. In DEFINE CLASS AS, I don't see a base class named window. Is it the right way to look at?

Use a form, and you can treat it as a window. In any window-related commands, it's form.name that equals window name:

o=createobject("form")
o.Name="xample"
show window xample

Then, of course, you can have your own form class that'll have any such properties that you may want.