who says that <ul>...</ul> positioned between </li>...<li> is invalid?
W3C Markup Validation Service :)
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" >
<title></title>
</head>
<body>
<UL>
<LI> examples/html: </LI>
<UL>
<LI> examples/html/bars: </LI>
</UL>
<LI> examples/ps: </LI>
</UL>
</body>
</html>
---
Validation Output: 1 Error
Line 11, Column 6: document type does not allow element "UL" here; ass
+uming missing "LI" start-tag