How to add an arrow for polyline in czml?

CesiumJS
1

Hi,All,
I can create polyline with arrow by set the material by code. However, in czml, there is no example to show how to add arrow. I see the document, Content in CZML, on wiki. Polyline have material property. But no description about how to create such material in Czml.

So, How to do it?

Thanks,
-Jonathan