xpath - Looking for n-th instance of x node in root node -

suppose have following xml

<root>     <x>         <y />         <z>             <y />         </z>         <n>             <m>                 <y />*             </m>         </n>     </x>     <x>         <y />         <z>             <y />         </z>         <y />*     </x> </root> 

i retrieve y nodes followed *

so third node in x ancestor node

i tried like:

//x//y[3] 

however doesn't work guess work if y nodes on same level.

so tried (//x//y)[3] retrieves 1 node (third one) in whole document

so tried like:

//x(//y)[3] //x(//y[3]) //x//(y[3]) 

etc. parse error

is there way retrieve need using xpath?

use:

//x/descendant::y[3] 

this selects every third y descendant of each x in document. helps write out expanded expression see what's going on. in case, following:

//x//y[3] 

is equivalent to:

/descendant-or-self::node()/child::x/descendant-or-self::node()/child::y[3] 

written way becomes obvious why doesn't wanted (i.e. it's looking y third child of x element , there isn't one). wanted every third y descendant. here expanded:

/descendant-or-self::node()/child::x/descendant::y[3] 

the important lesson here pays know xpath abbreviated syntax doing. spec quite readable. recommend taking look.