Holmes is stand-alone diagnostic CSS stylesheet that can highlight potentially invalid, inaccessible or erroneous HTML(5) markup by adding one class. holmes.css is useful for checking the quality of your code (up to W3C HTML5 standards), nitpicking over ensuring markup is valid and semantic and accessility guidelines are met, and when you are tasked to fix up and debug an old, OLD website. It has a simple implementation and a mostly unobtrusive effect on your page. Not recommended for live enviroments.