Error when trying to follow Deep learning example

Dears,   I strongly suspect that my question is rather fundamental and basic and less related to  Deep learning but because I wanted to highlight the context hence the title of this thread. Well, this is how I am trying to execute the "Word-By-Word Text Generation Using Deep Learning" example which uses text from Alice in Wonderland.   When calling:     ds = documentGenerationDatastore(documents); I get the error message:     'documentGenerationDatastore' is used in Word-By-Word Text Generation Using Deep Learning. The above message looks like an affirmative sentence, which of course I can agree with but it is a bit laconic. Does anyone perhaps know what is causing this error?