In general, the documentation follows the conventions as described in the following sections.
But ... please do not get overwhelmed by the vast amount of information and "rules". You can start writing documentation right away, before having read all this and learn as you go along! The sections in this chapter are meant to help you in this task and not make it excruciatingly difficult and tedious! When you make a change to the official documentation, there is always a maintainer who will check the changes. He or she may give you some friendly words of advice if something is not ok, but it is not a huge problem!