JError is shown as deprecated (as of 12.3), but is still widely used in the core. The API docs say that its status is deprecated - 4.0 Will be removed without replacement, but its still alive and well in 4.0.0 Alpha 1. Is it still being deprecated?
If it truly is deprecated and we are supposed to stop using it, what is the alternative for the following situation. In the save method of a component model subclassing JModelAdmin, and you want return false to indicate that there was a problem with the data, how do you add a message to the error box?