As someone who always used uppercase for tags back in the day, it wasn't about saving space; it was to improve human readability. All caps tags stood out better

As someone who always used uppercase for tags back in the day, it wasn't about saving space; it was to improve human readability. All caps tags stood out better against the backdrop of mostly lower case prose. Also the DOM APIs case-folded to upper when inspecting an HtmlElement object's name. To be honest, this is the first I heard that folks thought it had space advantages.