In valid XHTML you don’t see the mixed case or uppercase (she accepts case sensitive lowercase for those attributes). XHTML documents must use lower case for all HTML element and attribute names. This difference is necessary because XML is case-sensitive e.g. <li> and <LI> are different tags.
It also depends on the markup language, and rule of thumb is; always use lowercase for the META and its attributes; <meta name=“keywords” content=“…” /> would be the correct format. The value of the content, i.e. keyword list is also case-sensitive but can be mixed.
Thank you. I’ve seen the caps used often - it seems especially so on what I think of as “newer professional sites”. I thought it was a more current way of doing it for HTML5 or CSS5!
I think you meant CSS 3, as CSS 5 is even a twinkle in Paul’s eye. Usually it shows poor craftsmanship or pollution from an editor either liveware or software like both Ralph and Maleika mentioned if you get such ‘inconstancy’. Since those examples suggest attempted XHTML grammar they ought to be lower case. Even most HTML5 material recommends using lowercase. In the age of dinosaurs sometimes authors wrote uppercase for tags and lowercase for attributes but it was a pointless exercise.
Well, modern looking outwardly can drastically differ from the syntax under the hood so don’t always be fooled by visually stunning façades and the painted eyelids as they may be covering deeper cracks.