Subfields of documentation includes:
Documentation understood as document is any communicable material (such as text, video, audio, etc., or combinations thereof) used to explain some attributes of an object, system or procedure. It is often used to mean engineering documentation or software documentation, which is usually paper books or computer readable files (such as HTML pages) that describe the structure and components, or on the other hand, operation, of a system/product.
A professional whose field and work is documentation used to be termed a documentalist. Normally, documentalists are trained or have a background in both a specific subject and in the field of documentation (today information science). A person more or less exclusively to write technical documentation is called a technical writer. Technical writers are similarly trained or have a background in technical writing, along with some knowledge of the subject(s) they are documenting. Often, though, they collaborate with subject matter experts (SMEs), such as engineers.
Common types of computer hardware/software documentation include online help, FAQs, how-tos, and user guides. The term RTFM is often used in regard to such documentation, especially to computer hardware and software user guides.
A common type of software document frequently written by software engineers in the simulation industry is the SDF (software documentation folder). While developing the software for a simulator, which can range from embedded avionics devices to 3D terrain databases to full motion control systems, the engineer keeps a notebook detailing the development lifecycle of the project. The notebook can contain a requirements section, an interface section detailing the communication interface of the software, a notes section to detail the proof of concept attempts to track what worked or didn't work in solving certain problems, and a testing section to detail how the software will be tested to prove conformance to the requirements of the contract. The end result is a detailed description of how the software is designed, how to build and install the software on the target device, and any known weaknesses in the design of the software. This document will allow future developers and maintainers of the trainer to come up to speed on the software design in as short a time as possible and have a documented reference when modifying code or searching for bugs.