score:0

you can do that.

at first, highcharts has callback function.
https://stackoverflow.com/a/16191017

and modified version tipsy can show tooltip in svg.
http://bl.ocks.org/ilyabo/1373263
*use jquery.tipsy.js and tipsy.css on this page.

then, start highcharts like this.

$('#your-chart').highcharts(your_chart_options,function(chart){
    $('#your-chart').find('.highcharts-legend-item').each(function(){
        // set title text example
        var _text = $(this).text(),
            _title = '';
        switch(_text){
            case "legend 1":
                _title = 'legend 1 title';
                break;
            case "legend 2":
                _title = 'legend 2 title';
                break;
        }
        // add <title> tag to legend item
        $(this).append($('<title></title>').text(_title));
    });
    $('#your-chart').find(".highcharts-legend-item").tipsy({
        gravity: 's',
        fade: true
    })
});

score:5

there is another opportunity to get tooltips at hovering over the highcharts legend. you just need to enable usehtml for the legend and redefine the labelformatter function; this function should return the label text enclosed into the "span" tag. in this "span" tag one may include a class to apply jquery-based tooltips (jquery ui or bootstrap for example). also it is possible to transfer some data (for example, the index of a legend item) using the 'data-xxx' attribute:

labelformatter: function () {
    return '<span class="abc" data-index="' + this.index + '">' + this.name + '</span>';
}

tooltips can be formatted as you wish; hyperlinks are also possible. the fiddle is here.

score:10

highcharts doesn't have built-in tooltip for item legend, but still you can create your own tooltip for that. it's simple to add custom events to legenditem (mouseover and mouseout for example) and show that tooltip.

see example how to add events to elements in highcharts: http://jsfiddle.net/rasrp/129/

        events: {
            load: function () {
                var chart = this,
                    legend = chart.legend;

                for (var i = 0, len = legend.allitems.length; i < len; i++) {
                    (function(i) {
                        var item = legend.allitems[i].legenditem;
                        item.on('mouseover', function (e) {
                            //show custom tooltip here
                            console.log("mouseover" + i);
                        }).on('mouseout', function (e) {
                            //hide tooltip
                            console.log("mouseout" + i);
                        });
                    })(i);
                }

            }
        }

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