ex Page three girl arrested on suspicion of terror offences

ITV News have reported an ex page three girl has been arrested on terror charges. Read the article here. 

Having read this and it appears someone has been arrested for "possessing a document or record which contains information of a kind likely to be useful to a person committing or preparing an act of terrorism." Obviously there is more to this and the police are restricted in what they say.

I have a question :-
 What is a "document or record which contains information of a kind likely to be useful to a person committing or preparing and act or terrorism"?

  Not wishing to demean the subject at all, would an AtoZ and a Yellow Pages be useful? or a bus and train timetable? what sort of documents are we referring to?
  Or is it a wording thing? should it read contains a plan for an act of terrorism.

Genuine question, what does this all mean?