As used in SharePoint 2007 – putting a red wavy line below text in a text box. Neat.

Just in case I ever need this (and the page goes missing):

<style>
.squiggle
{
background-image:url("squiggle.gif");
background-repeat:repeat-x;
background-position:left bottom;
padding-bottom:2px;
vertical-align:text-top;
font-style:italic;
}
.container
{
border:1px solid #a5a5a5;
overflow-x: hidden;
width: 100%;
color: windowtext;
height: 18px;
background-color: window
}
</style>
<div class="container" contenteditable="true" tabindex="0">
<span class="squiggle" contenteditable="false" tabindex="-1">
<div style="DISPLAY: none" displaytext="here"></div>
<span contenteditable="true" tabindex="-1">unresolved!</span>
</span>
</div>