I found something wrong.

for ex:

<ul>

<li></li>

<li></li>

<li></li>

<li></li>

</ul>

The query:

$('ul:first li:last').filter('ul:first li:first')

return as $('ul:first li:last')

This problem cause: $('ul:first li:last').is('ul:first li:first') return true and many other functions using 'is' function will not be correct.

Please investigate this problem