IgnorePropTransientFor - bakkeby/dusk GitHub Wiki
If the IgnorePropTransientFor flag is set for a client then property notification events of type
XA_WM_TRANSIENT_FOR are ignored.
The effect of this property notification is that if the transient for hint of the window refers to another window that is also a client of the window manager, then the window will become floating.
This is considered to be a workaround for buggy client windows that do not behave correctly. An example case being WebStorm where the main window would randomly become floating.