Changes in HTML 5 - <u> Tag
The <u> tag was deprecated in HTML 4 and considered invalid in later versions, but has now been added back into the WHATWG HTML Living Standard and W3C HTML 5 (after the two versions diverged - see difference between HTML 5 and HTML Living Standard). Therefore, whether or not the u element is valid depends on the version of HTML:
- HTML 2 and earlier - <u> tag did not exist
- HTML 3.2 - <u> tag added
- HTML 4 - <u> tag deprecated, invalid in HTML 4 strict DTD
- XHTML - <u> tag invalid
- WHATWG HTML 5 - u element invalid
- WHATWG HTML Living Standard - u element added
- W3C HTML 5 - u element added