Is it possitble to know the names of the Fields in a downloaded AllenNLP model?

For example,
If I download a masked language model from the internet, is it possible to know the names of the “Fields” of the “Instance”?

archive = load_archive(cached_path(''))
predictor = Predictor.from_archive(archive, "masked_language_model")

is it possible to print out vocab namespace/ Fields name for an input instance?

Found my answer. I was looking for a vocab namespace. I will leave my solution here in case someone has the same problem.