Why is the underline (U) icon in the property inspector of text absent, whereas the Bold (B) and Italics (I) icons are present?

Keith,

This is a crucial part of usability control.

Adobe (and Macromedia before them) have purposely left out the (U) underline icon on the property inspector so that developers and designers do not apply the underline style to text that is not a link.

Nearly all people who use the web know that underlined text is clickable and will take them to a new page with more information about the text they just clicked on.

Breaking that fundamental rule will confuse (and frustrate) your visitors.

It is possible to underline text using the <U> tag, and also setting the CSS style parameter text-decoration: underline;, but you should only do this if the text is a link. And you shouldn't need to apply the underline style because most browsers automatically apply the underline.

I've seen headings before that are underlined because they were headings. This is wrong. Designers have italics, bold, colour or size increase to indicate headings, and should use these instead. Headings should also use the heading tags (H1, H2, H3 etc) to properly indicate the structure of the web page.

I'd recommend reading the following articles:
http://www.useit.com/alertbox/20040510.html
http://www.useit.com/alertbox/designmistakes.html
Jakob's other 'design mistakes' are also well worth reading.

I hope this clears up the confusion, Keith. I hope you enjoyed your Dreamweaver training with us today.

Regards, Rich