Text Key for Invalid Label

We're trying to modify the text key that shows if a user enters an invalid label (one that hasn't been pre-defined, in this case), when creating a new blog post but we want to keep the variable that shows the invalid label. Right now the error message is "The following labels are not available here: labels, go, here". The text key that displays is "error.message.labels.label_not_from_predefined_list". Editing that text key changes the error message, but we still want to list the invalid labels if possible. I'm assuming this is a variable that needs to go in { }, but I can't find any docs about this. Does anyone know what that variable is or how to find it?

Thanks!

Nathan