# Style guide ## Source file headers All source files must include a standard header. An example of a typical header : ```asm ; SPDX-License-Identifier: GPL-2.0-only ; Copyright © 2024-2025 KolibriOS team ; Copyright © 2020 Acme Inc. ; ; Extended maths functions for Calc+ calculator. ; ``` No single line in the header should exceeds 80 characters. The first line of the file header should always be the SPDX License Identifier, unless there is a technical restriction (e.g. the `#!` shebang in script files), in which case it should be on the next available line. The Identifier should match the accepted values by [SPDX](https://spdx.org/licenses/). Where the license is unknown, it should be marked as `NOASSERTION`, until determined by the authors and/or copyright holders, or other sources. Do not mark the file as GPL without _absolute certainty_. Many licenses are incompatible and should be a consideration for authors selecting the correct license for their work. The next lines should include any relevant copyright information, with the first typically being an attribution to `KolibriOS team`, which will cover most contributors. Currently this is _not_ formatted as a detailed SPDX comment per [REUSE software](https://reuse.software) initiative from FSFE. A simpler header is preferred for human readability. With exception for the principle copyright statement, a single date for the earliest claim is preferred to a range. More details on formatting copyright can be found [here](https://matija.suklje.name/how-and-why-to-properly-write-copyright-statements-in-your-code). In rare cases where the copyright is unknown, it should be marked as `Copyright NOASSERTION`, until determined otherwise. Avoid including Contributor attributions, which bloat the header. This information should be included in the commit messages of the Version Control System, which provides a sufficient audit trail (e.g. git blame). A final one sentence comment should be included which defines the purpose of the file or program.