It’s generally not a good typographic practice to use the default underline function in most applications including the <u> tag in HTML. Many designers believe that underling is not an appropriate method for adding emphasis to text.  It’s a holdover from the days of typewriters when other forms of emphasis, like bold text or different colors, were not available. On the web there is a convention that underling denotes a hyperlink so many web designers feel that underling should only be used to represent hyperlinks. Website users may get confused if they click on underlined text that is not a link. Bold ( <strong> in html) or italics (<em> in html) are more valid ways of emphasizing text. In HTML the <u> element, used for underlining,  was deprecated in HTML 4.01. It returned in HTML 5 but has a different semantic meaning.