The phrase "official handbook" refers to a book or guide that is authorized and recognized as being trustworthy and accurate in providing information on a certain topic. Full definition
«It comes as no surprise that a man who couldn't even pay his own council tax bill can't be bothered to read his own official handbook,» said shadow local government minister Caroline Spelman. (politics.co.uk)
It concludes that the trust was therefore in breach of the Academies Official handbook, the Charities Commission Statement of Recommended Practice and the Academies Accounts Direction. (bbc.co.uk)
On the converse, DOC / DOP / IPG / SGT marks are reserved to products following specific regulations (actually official handbooks, disciplinary guidelines) that mostly require their ingredients come from local land. (law.stackexchange.com)