business logic - jQuery end(), where exactly it is useful -

i have looked in jquery documentation of function end(),

definition : end recent filtering operation in current chain , return set of matched elements previous state.

i have understood functionality, not able make out, more helpful.

ex:

<p>text</p> <p class="middle">middle <span>text</span></p> <p>text</p>  <script type="text/javascript"> alert(jquery('p').filter('.middle').length); //alerts 1 alert(jquery('p').filter('.middle').end().length); //alerts 3 alert(jquery('p').filter('.middle').find('span') </script> 

i have understood second line displaying //alerts 3 , can written as

 alert(jquery('p').length); //alerts 3 

then why 2 methods .filter , .end() ,

please give me example, .end() useful.

html

<p>text</p> <p class="middle">middle <span>text</span></p> <p>text</p> 

in p tag sibling element

and pwith class "middle" has child tag "span" tag

now talk js

     <script type="text/javascript">          /*it display 1 , right first find p tag in filter "middle class"          , in p tag 1 have class alert  1        */  alert(jquery('p').filter('.middle').length);          /*it display 3 , right first find p tag in filter "middle class" again use end inn jquery again goes previous selector means       (jquery('p').filter('.middle') jquery('p')       alert 3                   */  alert(jquery('p').filter('.middle').end().length); //alerts 3      /*it display 3 , right first find p tag in filter "middle class" again use find span , has 1 span in middle class alert 1     */          alert(jquery('p').filter('.middle').find('span').length); alert 1         </script> 

reference end

find

filter