带有u标签的Span标签

Question

I am having a problem with a span tag and a underline tag. I dont understand why I can't add a underline tag within a span tag.

Why would I be able to add i tag but not the u tag?

<span>aa bb cc 
<u>
<strong>AND</strong>
</u> 
aa bb cc </span>

The element 'span' in namespace ' http://www.w3.org/1999/xhtml ' has invalid child element 'u' in namespace ' http://www.w3.org/1999/xhtml '. List of possible elements expected: 'a, br, span, bdo, map, img, tt, i, b, big, small, em, strong, dfn, code, q, samp, kbd, var, cite, abbr, acronym, sub, sup'

Answer 1

Because underlining is widely used for hyperlinks on web sites, the general recommendation is not to use underline for text decoration. This, however, shouldn't keep anyone from using underline, but only serve as a recommendation that you use underline with care, so the reader intuitively can see that it is an underline, not a hyperlink.

Underline can be done in two ways:

The tag <u> or style="text-decoration:underline" .

Style needs to be applied on a tag which is a text section, eg <p>, <div> and <span>. The way underline is normally used in text, will usually be a good solution. As far as I have tested the two ways of underlining, they give exacly the same effect, also in combination with other styles.

Officially HTML 5 does not support the u tag, and when validating the code a warning or error message will appear, but the underline appears without any problems.

Answer 2

I don't think there's anything wrong with your code. It passes the W3C validation check here: https://validator.w3.org/nu/#textarea