# chickadee » mistie » mistie-def-ctl-seq

##### Identifier search
mistie-def-ctl-seq SEQ WRITERprocedure

This Mistie procedure defines control sequences. A control sequence is a sequence of letters (alphabetic characters), and is invoked in the input document by prefixing the sequence with an escape character. The case of the letters is insignificant.

mistie-def-ctl-seq associates a procedure with a control sequence -- when the control sequence SEQ occurs in the input document, it causes the procedure WRITER to be applied.

The following defines the control sequence br, which emits the HTML tag <br>:

```(mistie-def-ctl-seq 'br
(lambda ()
(display "<br>")))```

Before a control sequence can be used, we must fix the escape character. The following sets it to backslash:

`(set! mistie-escape-char #\\)`

We can now invoke the br control sequence as \br.