# What exactly "subset" is in "tf.keras.preprocessing.text_dataset_from_directory"?

so I'm following the official keras tutorial here. However I couldn't really understand the subset and validation_split arguments of tf.keras.preprocessing.text_dataset_from_directory.

How I use them is:

raw_train_ds = tf.keras.preprocessing.text_dataset_from_directory(
"aclImdb/train",
batch_size=BATCH_SIZE,
validation_split=0.2,
subset="training",
seed=1337
)

raw_val_ds = tf.keras.preprocessing.text_dataset_from_directory(
"aclImdb/train",
batch_size=BATCH_SIZE,
validation_split=0.2,
subset="validation",
seed=1337
)


As I understand we're trying to split train data into validation of its 0.2. However we do the same for both "training" and "validation" subsets on same dataset with the same validation_split value which is 0.2. So isn't it supposed to take 0.2 of training data to raw_train_ds and 0.2 to raw_val_ds instead of 0.8, 0.2?

I checked the documentation from here which was not really useful. I also couldn't find any related questions. How does this work exactly?