In XHTML Strict, it seems that you're not allowed to use the <u> tag any more. Is there a semantic equivalent like there is for <b> and <i>? If not, is there any convention for how to markup underlined text in XHTML?
Thanks.
In short - no.
<b> and <i> don't really have equivalents, either. It's all about the separation of content and appearance. The goal of XHTML strict is that the XHTML markup should be used to describe the structure of the content.
<em> tags are used to convey emphasis and <strong> tags are used to give strength to the content. It just so happens that the default style sheet in most browsers equates these to italic and bold respectively.
Having a direct equivalent for bold, italic and underline in XHTML would allow people to dictate the appearance of the content too closely. Ideally, you should think about why you want a piece of text to stand out, define that in the structure and then leave the CSS boys to decide how it should ultimately be rendered.