Sometimes you don't have space on the screen to put a label, or that label would interfere with the design. Or, you might need to put two labels on a single control. Screen readers will read the title on form controls. The title also appears as a tooltip when the mouse hovers over the control, so it can function like a hint for some users.
Title attribute
<form>Heydonworks tooltip,
<form>
<label for="zip">Zip Code:</label>
<input name="textfield" size="5" id="zip" type="text" /> -
<input name="textfield2" size="4" type="text" aria-describedby="zip-tip"/>
<div role="tooltip" id="zip-tip">4 extra numbers in zip-code</div>
</form>
{CSS}
[role="tooltip"]
{
display: none;
padding: 0.15em;
margin: 0;
color: #fff;
background: blue;
width: 100%;
z-index: 2;
}
input:focus + [role="tooltip"], input:hover + [role="tooltip"]
{
display: block;
top: 100%;
position: relative;
}