function text_size(factor)
{
    var $el = $('.body');
    var re = /([0-9]+)([a-zA-Z]+)/;

    var size = $el.css('font-size');
    var msize = re.exec(size);
    if (msize.length != 3)
        return;
    var newsize = parseInt(msize[1]) + factor;
    $el.css('font-size', newsize + msize[2]);

    var lheight = $el.css('line-height');
    var mlheight = re.exec(lheight);
    if (mlheight.length == 3 && mlheight[2] == msize[2])
    {
        var diff = parseInt(mlheight[1]) - parseInt(msize[1]);
        $el.css('line-height', newsize + diff + msize[2]);
    }
}