What does "plain" mean in preprocess.sh ?

[Aolius]

Hi, thanks for sharing your code with us.

I wonder what the SPLIT "plain" means in preprocess.sh:

https://github.com/GT-SALT/FormalityStyleTransfer/blob/a86d287d0c48238f7cd39f6f34b465b0b7ccb2f4/preprocess.sh#L6

https://github.com/GT-SALT/FormalityStyleTransfer/blob/a86d287d0c48238f7cd39f6f34b465b0b7ccb2f4/preprocess.sh#L26

Also, the preprocess.sh script requires files named like "train.source" and "val.target". The GYAFC dataset does not follow this format, however. Should I reformat the original files into the required format? In that case, which files should be renamed "plain.source" and "plain.target"?