One thing that struck me while attending Ed Burns' JSF talk about JSF 2.3 at JavaOne 2017 was a comment he made that autocompletion isn't working in Netbeans for JSF 2.3 features. I would describe this as NetBeans 8.2 showing "angry red" for components it doesn't understand, such as f:validateWholeBean.
As in the attached screenshot, an example error is "The component library Jsf Core does not contain component validateWholeBean".
In the past, NetBeans releases were coordinated with Java EE releases. When Java EE 8 came out, I expected that NetBeans 9 would come out and support JSF 2.3. When we onboard new developers, I would rather not say to them, "It's ok to see angry red like this in NetBeans."
Incidentally, during Ed's talk I asked if he knew if JSF 2.3 is supported by IntelliJ or Eclipse and he wasn't aware if they support it or not.
 Contemporary Java Web Applications with JSF 2.3 - https://www.youtube.com/watch?v=yshXLB_HdhU