Read the up-to-date documentation: 
-no_xhtml

    By default, CGI.pm versions 2.69 and higher emit XHTML (http://www
+.w3.org/TR/xhtml1/). The -no_xhtml pragma disables this feature. Than
+ks to Michalis Kabrianis <kabrianis@hellug.gr> for this feature.

    If start_html()'s -dtd parameter specifies an HTML 2.0 or 3.2 DTD,
+ XHTML will automatically be disabled without needing to use this pra
+gma.

[download]

update: my CGI.pm does the correct thing for that code (slightly fixed so it can be run without editing): 

use CGI;
my $query = CGI->new;
print $query->header(-type=>'text/html', -declare_xml=>0);

print $query->start_html(-title=>'Blah blah blah.',
    -background=>"../images/$SiteName.background.jpg",
    -link=>'brown',
    -vlink=>'#8b4513',

    -style=>{'src'=>"$SiteName.styles.css"},
    -script=>{ -language=>'JavaScript', -src=>"$SiteName.scripts.js" }
);

[download]
output: 
Declare-xml: 0
Content-Type: text/html; charset=ISO-8859-1

<!DOCTYPE html
        PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-U
+S">
<head>
<title>Blah blah blah.</title>
<link rel="stylesheet" type="text/css" href=".styles.css" />
<script src=".scripts.js" type="text/javascript"></script>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1
+" />
</head>
<body link="brown" vlink="#8b4513" background="../images/.background.j
+pg">

[download]
Note that you actually should not use declare_xml as a parameter to header() but to start_html().
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: XML tags using perl CGI by Joost
in thread XML tags using perl CGI by pmcaveman

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