Enum for dataset splits.
Datasets are typically split into different subsets to be used at various stages of training and evaluation.
TRAIN: the training data.
VALIDATION: the validation data. If present, this is typically used as evaluation data while iterating on a model (e.g. changing hyperparameters, model architecture, etc.).
TEST: the testing data. This is the data to report metrics on. Typically you do not want to use this during model iteration as you may overfit to it.
ALL: Special value, never defined by a dataset, but corresponding to all defined splits of a dataset merged together.
See the guide on splits for more information.