Why is the TextDataset designed like this?

[jonflynng]

I came across this library reading the xFinance article. It claims that it continued the training of a pre-trained model in an unsupervised way with xTuring via the TextDataset. I'm struggling to understand why the TextDataset takes both a list of inputs and targets as logically it should just take a big block of text for further NSP training I think? What should it look like if wanting to replicate what the article discusses?