Another W3C recommendation relates to HTML attribute values. It would be best if you always put them in quotes. Plus, there are cases when you MUST use quotes. When a value contains spaces, apostrophes ('), equals signs (=), less than or greater than signs (<,>), and quotation marks ("), the code won't work without a proper markup. Also, using quotes around attribute values makes your code consistent and excuses you from memorizing and recalling the rules when quotes are optional.