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### The ` append-to-buffer ` Interactive Expression

Since the ` append-to-buffer ` function will be used interactively, the function must have an ` interactive ` expression. (For a review of ` interactive `, see section Make a Function Interactive.) The expression reads as follows:

```(interactive "BAppend to buffer: \nr")
```

This expression has an argument inside of quotation marks and that argument has two parts, separated by `\n'.

The first part is `BAppend to buffer: '. Here, the `B' tells Emacs to ask for the name of the buffer that will be passed to the function. Emacs will ask for the name by prompting the user in the minibuffer, using the string following the `B', which is the string `Append to buffer: '. Emacs then binds the variable ` buffer ` in the function's argument list to the specified buffer.

The newline, `\n', separates the first part of the argument from the second part. It is followed by an `r' that tells Emacs to bind the two arguments that follow the symbol ` buffer ` in the function's argument list (that is, ` start ` and ` end `) to the values of point and mark.

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