Someone

code:
...
<ul style="border: 1px solid black; list-style-type: none; padding: 0; margin: 0;">
<li style="float: left; border: 1px solid red;"><a href="#">Item three</a></li>
</ul>...

output:

http://img301.imageshack.us/my.php?image=screenshotfirefoxhu7.png

with LI styled with "float:left;" it goes outside of UL. it's kinda weird...why does this happens?