modelines

Modelines are lines embedded in a text file that allow a text editor to apply settings automatically when the file is opened. They are most commonly associated with Vi and Vim, but variants exist in other editors. A modeline specifies options such as tab stops, indentation method, text width, encoding, line endings, and filetype.

In Vim, a modeline is a line that starts with vim: or vi:, and is recognized if it appears within the first five or last five lines of the file. A typical Vim modeline uses the set command, for example: vim: set ts=4 sw=4 expandtab et: or vim: set ft=python ts=4 sw=4: The colon is used to delimit commands; multiple options can be listed separated by spaces. The editor applies these settings on opening the file.

Security considerations: Modelines can execute editor commands, which creates a potential risk if the file is from an untrusted source. Many editors provide a toggle to disable modelines (for example, set nomodeline in Vim) or restrict the commands that can be run. Newer configurations may enable strict parsing or disable evaluation of expressions within modelines by default.

Emacs and other editors offer similar per-file configuration mechanisms, such as Local Variables blocks at the end of a file, but they are not called modelines in the Vim sense.

See also: Local variables, file metadata, Vim modeline security.