Question

I was learning XPath using the following xml document: http://www.w3schools.com/xpath/xpath_examples.asp

Now, when I execute the query:

bookstore/book/author[contains(.,'G')]

I get the result: Giada De Laurentiis, James McGovern as expected. Now, since contains() returns a boolean value, I expected the following query to return all authors:

bookstore/book/author[true]

however, it returns an empty set. Can somebody explain?

Answer 1

I expected the following query to return all authors:

bookstore/book/author[true]

however, it returns an empty set. Can somebody explain?

The above expression selects all bookstore/book/author elements that have a child element named true. In the provided XML document no author element has a child named true — therefore the XPath expression selects nothing.

In a comment the OP asks:

But why does bookstore/book/author[true] not work, since if is
similar to the situation when the contains() always returns true

contains() never returns (the string) “true” — it returns the boolean value true() — this is different from the string “true”.

Explanation:

You are confused by the fact that the serialization of the boolean value true() to sting is the string “true”.

This fact doesnt mean that the string “true” and the boolean value true() are identical.