Actually, if you look at the source for CGI::start_html(), you'll see that an ordered hash would make no difference.

for(    start_html({
            -title => "title",
            -style => {
                -src => [
                    "/$common_css",
                    "/$css",
                    "/$common_cal_css",
                    "/$cal_css",
                    "/ie.css",
                ],
            },
        })
) {
    s{(<[^>]+/ie\.css[^>]+>)}{<!--[if IE]>$1<![endif]-->};
    print;
}
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