I don't think it was ever case sensitive. I'm pretty sure that in 1994, I was using lower case html tags without issue at university in Mosaic. Netscape Navigat

I don't think it was ever case sensitive. I'm pretty sure that in 1994, I was using lower case html tags without issue at university in Mosaic. Netscape Navigator definitely allowed you to use lower case tags. My final year project was littered with mixed case tags.