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Automatic selection: Behind the scenes

Emacs determines the major mode as follows:

  1. First line1 is scanned for -*- mode: NAME -*- string.
  2. File name is matched against auto-mode-alist in .dir-locals.el.
  3. Shebang (#!) is matched against interpreter-mode-alist.
  4. Beginning of the buffer content is matched against magic-mode-alist.
  5. File name is matched against auto-mode-alist.
  6. Beginning of the buffer content is matched against magic-fallback-mode-alist.

Footnotes:

1

If the first line is a shebang, the second line is scanned.

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