WindowScope
The receiver of the content of a Window and of a Dialog: the window that content fills.
What a window carries besides its content is declared on this scope, so such a declaration is only available where there is a window to carry it. MenuBar and GlassPane are such declarations: each reaches the window whose content it is composed in, and a call to either anywhere else does not compile.
A scope is received, never made: every value of this type is one a window handed its content, so a declaration made on it reaches the window that content is in and no other.