It's obvious student's book hasn't been formatted (9)

I believe the answer is:

plaintext

I'm a little stuck... Click here to teach me more about this clue!

'hasn't been formatted' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'it's obvious student's book' is the wordplay.
'it's obvious' becomes 'plain' (similar in meaning).
'student's book' becomes 'text' (I've seen this in another clue).
'plain'+'text'='PLAINTEXT'

Can you help me to learn more?

I've seen this clue in The Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.