this does not work:
dataset = datasets.load_dataset('mc4','iw',split='train+validation',streaming=True)
with error:
ValueError: Bad split: train+validation. Available splits: ['train', 'validation']

these work:
dataset = datasets.load_dataset('mc4','iw',split='train+validation')
dataset = datasets.load_dataset('mc4','iw',split='train',streaming=True)
dataset = datasets.load_dataset('mc4','iw',split='validation',streaming=True)

i could not find a reference to this in the documentation and the error message is confusing. also would be nice to allow streaming for the merged splits