...for obvious reasons...
com.gluonhq.charm.glisten.mvc.View is no standard JavaFX control.
To make that class known to Scene Builder we just need to put it on its classpath. Right? The following screenshots describe a workaround when using NetBeans. If there are other, less archaic approaches, I'd love to hear them.
First we need the .jar file.
Now comes the interesting part. How to tell Scene Builder?
There is a config file called SceneBuilder.cfg. On my Windows machine it's situated in C:\Users\tkuen\AppData\Local\SceneBuilder\app.
Just quit Scene Builder and then put the fully qualified path right beside app.classpath=.
Here is how Scene Builder will render another .fxml file contain Glisten controls.
I do not consider myself a Scene Builder expert, so I may be missing a simpler solution. Also, it would be great to have custom components in the palette. Need to check that. Again, any hint is greatly appreciated.