It is a JMP Pro feature. Do you have JMP Pro? Are you using JMP Pro?
It is used in marginal model inference for mixed models. Are you fitting a mixd model Are you using this inference?
There is more than one plot for this exploration./ Which plot are you using?
What are you trying to do?
What model are you trying to fit and evaluate?
What is your source of data?
What is your analytic problem?
Who needs an explanation?
What is the background of the people who need the explanation?
What is your backbround in mixed models?