### The First Line of a Texinfo File

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 is usually located in the `/usr/lib/tex/macros' directory. TeX uses the backslash, `\', to mark the beginning of a command, just 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.