A DESCRIPTION OF THE REQUEST :
At the moment the user can create windows using JavaFX, which will not be shown in the taskbar, but will be decorated with the window manager (StageStyle.UTILITY). Alternatively, it is possible to create undecorated windows that will have their own button in the taskbar (StageStyle.UNDECORATED, StageStyle.TRANSPARENT).

However, there are situations when you need to create a window without decorations, which will not be displayed on the taskbar. At the moment, JavaFX does not provide any possibility for this.

In this case, the toolkit itself is capable of this (the styleMask field of the com.sun.glass.ui.Window class has a combination of flags that allow this behavior to be implemented).

JUSTIFICATION :
There are situations when it is necessary to create a window that will not have any decorations, or buttons on the taskbar. For example, different screen widgets, as well as notifications.

This functionality is available in all popular graphics libraries (Swing, Qt, etc.).

I think that this functionality is not difficult to add.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Additional styles for the Stage or something else, allowing you to create windows of the following types:

1) Window without decorations and hidden from the taskbar (styleMask = UNTITLED | UTILITY)
2) Transparent window without decorations (styleMask = UNTITLED | UTILITY | TRANSPARENT)
ACTUAL -
You can create only a decorated window hidden from the taskbar.

CUSTOMER SUBMITTED WORKAROUND :
You can create a window using Swing (which supports the required functionality), and then put a JavaFX component in it. However, such a solution may have performance problems. In addition, the Swing transparency mechanism has its drawbacks (for a full-fledged custom shaped window under Linux, a call to setShape is required, which wants for the vector outline of the window, which is not always available simply). Also I think JavaFX should be a self-sufficient toolkit.