This option enables you to specify that list elements UL/OL is to be converted to valid XHTML. This option is disabled by default.
This invalid list:
<ol>
<li>a</li>
<ol>
<li>b</li>
<li>c</li>
</ol>
<li>e</li>
</ol>
Gets converted into this valid list:
<ol>
<li>a
<ol>
<li>b</li>
<li>c</li>
</ol>
</li>
<li>e</li>
</ol>
Example of usage of the fix_list_elements option:
tinyMCE.init({
...
fix_list_elements : true
});