I'm using a jquery function I found to find words in a div and highlight them. I'm using this along with a search tool so the case is not always going to match the words exactly. How can I convert this to make it case insensitive?

$.fn.highlight = function(what,spanClass) {

    return this.each(function(){

        var container = this,

            content = container.innerHTML,

            pattern = new RegExp('(>[^<.]*)(' + what + ')([^<.]*)','g'),

            replaceWith = '$1<span ' + ( spanClass ? 'class=' + spanClass + '' : '' ) + '>$2</span>$3',

            highlighted = content.replace(pattern,replaceWith);

        container.innerHTML = highlighted;

    });

}