3.2.1 The First Line of a Texinfo File
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Every Texinfo file that is to be the top-level input to TeX must begin
with a line that looks like this:

\input texinfo   @c -*-texinfo-*-

This line serves two functions:

1. When the file is processed by TeX, the `\input texinfo' command
tells TeX to load the macros needed for processing a Texinfo file.
These are in a file called `texinfo.tex', which should have been
installed on your system along with either the TeX or Texinfo
software.  TeX uses the backslash, `\', to mark the beginning of
a command, exactly as Texinfo uses `@'.  The `texinfo.tex'
file causes the switch from `\' to `@'; before the switch
occurs, TeX requires `\', which is why it appears at the
beginning of the file.

2. When the file is edited in GNU Emacs, the `-*-texinfo-*-' mode
specification tells Emacs to use Texinfo mode.


