A letter is an official document used to discuss work, ask and answer questions, and request approval and reply to approvals between unaffiliated organs. A letter is a parallel document and cannot be used in subordinate or superior organs. Letter as the only official document in a parallel text, the scope of its application is quite wide. In the direction of execution, not only can be executed between parallel organs, but also can be executed between organs that are not subordinate to each other, including superior organs or subordinate organs. In terms of the applicable content, it is mainly used for the unaffiliated organs to consult with each other on work, inquiries and replies to questions, but also for requesting approval from the competent authorities concerned, inquiring about specific matters from higher-level organs, and for higher-level organs to reply to inquiries or requests for approval from lower-level organs, as well as for higher-level organs to call for the handling of relevant matters of lower-level organs, such as requesting lower-level organs to report statements, materials, statistics, etc. by letter. In addition, the letter can sometimes be used for the superior organ to reply to the inquiry or request approval of the inferior organ. In addition, the letter can sometimes be used for the higher authorities on a piece of original documents to make smaller additions or corrections. But this situation is not rare.
Request for instructions is an official document that "applies to the higher level to request instructions, approval". It is a superior document. Any matter that the organization does not have the authority or power to decide or solve can be requested from the higher level, and the higher level should reply in time. It is a common style in the practice of applied writing. Requests for instructions can be divided into three kinds. Request for instructions, request for approval, request for approval.