Need help with xpath expression

[C Wong]

I would appreciate if someone could explain the following expression in plain English, if possible:
- select="//a[not(following::x=.)] | //x[not(preceding::a=.)] "
- select="//a[not(preceding::a=.)]" - (e.g. select unique value of a ??)
source: Whizlabs

[Vivek Saxena]

You can find your answer here.
VivekS.

[C Wong]

Thanks... but I still have doubts on the first part of the logic. - //a[not(following::x=.)].
Following Roseanne's suggestion, I interpret the logic as: Select all a elements which have x in its following axis and the node value of x does not equal to the node value of a.
My answer: 1 (from 1st B-set) 3 2 3 (from 2nd B-set). But the correct answer is 3 2 3 only!!
May be my interpretation is wrong!! Please help.

[Vivek Saxena]

XML File

<Root>
<B>
<a>1</a>
<a>2</a>
<a>1</a>
<x>3</x>
<x>4</x>
<x>2</x>
</B>
<B>
<a>3</a>
<a>1</a>
<a>2</a>
<a>3</a>
<x>5</x>
<x>4</x>
<x>1</x>
</B>
</Root>

I would say
“
Select all ‘a’ elements which have x in its following axis and the node value of ‘a’ node does not equal to the node value of ‘x’ in its following axis.
“
So My answer:
1st , 3rd and 4th node in second B-set. Which are basically 3,2,3
If I can be of further assistance, please let me know.
NOTE: For future I would suggest you to post full question including all the files. Just a suggestion.
Thanks
VivekS

[C Wong]

Vivek, I believe I almost get it. The reason that <a>1</a> from the first B-set is rejected is because there is <x>1</x> following in the 2nd B-set. In other words, "following" does not stop at the B-set, it stops at the end of file. Please confirm my understanding is correct. Thanks.

[Vivek Saxena]

Yes you are absolutely correct!