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
});