chickadee » chicken » read-syntax » #!

#!read
#!... 

Interpretation depends on the directly following characters. Only the following are recognized. Any other case results in a read error.

Line Comment
If followed by whitespace or a slash, then everything up the end of the current line is ignored
Eof Object
If followed by the character sequence eof, then the (self-evaluating) end-of-file object is returned
DSSSL Formal Parameter List Annotation
If followed by any of the character sequences optional, rest or key, then a symbol with the same name (and prefixed with #!) is returned
Read Mark Invocation
If a read mark with the same name as the token is registered, then its procedure is called and the result of the read-mark procedure will be returned