We've fixed the problem and validation-api is not required. Please try with the latest tagged M5.
Thanks for your response,
Yes I noticed that with 188.8.131.5201226-M5 validation-api is not required, but my warning was that if by inattention you put the validation-api without an implementation any input doesnt work silently without messages or Exceptions. May be a little confusing and dangerous ? Probably you should have an Exception something as "couldnt find a default provider". Dont forget also to remove the dependency validation-api.jar in the readme.txt.
For my other problem, i looked in the preliminary documentation and I could not see if a panelMenuItem can have an action or not !
I dont see any news in M5 or later for the rich:columns component, its a very useful component. I know that in many cases you could use c:forEach but its not very convenient and sometime you have strange problems with jstl tag that arent not real components.
Good luck for your release.
It works now with the released M5, if you put validation-api without an implementation you have the Exception "Unable to find a default provider"