CREATING THE HTTP HEADER: 

	print $query->header;


	     -or-


	print $query->header('image/gif');


	     -or-


	print $query->header('text/html','204 No response');


	     -or-


	print $query->header(-type=>'image/gif',
			     -nph=>1,
			     -status=>'402 Payment required',
			     -expires=>'+3d',
			     -cookie=>$cookie,
			     -Cost=>'$2.00');

header returns the Content-type: header. You can provide your own MIME type if you choose, otherwise it defaults to text/html. An optional second parameter specifies the status code and a human-readable message. For example, you can specify 204, ``No response'' to create a script that tells the browser to do nothing at all. If you want to add additional fields to the header, just tack them on to the end: 

    print $query->header('text/html','200 OK','Content-Length: 3002');

The last example shows the named argument style for passing arguments to the CGI methods using named parameters. Recognized parameters are -type, -status, -expires, and -cookie. Any other parameters will be stripped of their initial hyphens and turned into header fields, allowing you to specify any HTTP header you desire.

Most browsers will not cache the output from CGI scripts. Every time the browser reloads the page, the script is invoked anew. You can change this behavior with the -expires parameter. When you specify an absolute or relative expiration interval with this parameter, some browsers and proxy servers will cache the script's output until the indicated expiration date. The following forms are all valid for the -expires field: 

	+30s                              30 seconds from now
	+10m                              ten minutes from now
	+1h                               one hour from now
	-1d                               yesterday (i.e. "ASAP!")
	now                               immediately
	+3M                               in three months
	+10y                              in ten years time
	Thursday, 25-Apr-96 00:40:33 GMT  at the indicated time & date

(CGI::expires() is the static function call used internally that turns relative time intervals into HTTP dates. You can call it directly if you wish.)

The -cookie parameter generates a header that tells the browser to provide a ``magic cookie'' during all subsequent transactions with your script. Netscape cookies have a special format that includes interesting attributes such as expiration time. Use the cookie method to create and retrieve session cookies.

The -nph parameter, if set to a true value, will issue the correct headers to work with a NPH (no-parse-header) script. This is important to use with certain servers, such as Microsoft Internet Explorer, which expect all their scripts to be NPH.