wow... i didn't know that, for
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://
www.w3.org/TR/html4/loose.dtd">

<span style="width: 100px; background: yellow">a</span>b
<div style="width: 100px; background: yellow">a</div>b

1) the a and b will stick together for the first line, so span doesn't
honor the "width: 100px"

2) the div honors the "width: 100px", as the background is shown
yellow. but it will force a line break both before the div and after
the div.