What is the difference between normalize-space(.) and normalize-space(text())?

Question

I was writing an XPath expression, and I had a strange error which I fixed, but what is the difference between the following two XPath expressions?

"//td[starts-with(normalize-space()),'Posted Date:')]"

and

"//td[starts-with(normalize-space(text()),'Posted Date:')]"  

Mainly, what will the first XPath expression catch? Because I was getting a lot of strange results. So what does the text() make in the matching? Also, is there is a difference if I said normalize-space() & normalize-space(.)?

Solution

Well, the real question is: what's the difference between . and text()?

. is the current node. And if you use it where a string is expected (i.e. as the parameter of normalize-space()), the engine automatically converts the node to the string value of the node, which for an element is all the text nodes within the element concatenated. (Because I'm guessing the question is really about elements.)

text() on the other hand only selects text nodes that are the direct children of the current node.

So for example given the XML:

<a>Foo
    <b>Bar</b>
  lish
</a>

and assuming <a> is your current node, normalize-space(.) will return Foo Bar lish, but normalize-space(text()) will fail, because text() returns a nodeset of two text nodes (Foo and lish), which normalize-space() doesn't accept.

To cut a long story short, if you want to normalize all the text within an element, use .. If you want to select a specific text node, use text(), but always remember that despite its name, text() returns a nodeset, which is only converted to a string automatically if it has a single element.

Comments

[CJ7]

From my own testing normalize-space() and normalize-space(.) have the same effect.

[Matthijs Bierman]

Actually normalize-space(text()) will return an empty string, because it takes the text in the root. normalize-space(//text()) will return Foo, because it transforms your NodeSet by taking the first node and converting it to a String and running normalize-space on that.

[biziclop]

@Matthijs Bierman Have you tried it? I have and it works exactly as I said. (In Xpath 2.0, I shall add and assuming that the context node is the <a> element.)

[Matthijs Bierman]

Yes, I have (I wasn't sure). But I tried in XPath 1.0. Standard JAXP, but with Xerces 2.11.0 :).

[biziclop]

@Matthijs Bierman Weird, I'll experiment a bit with that. I know that my answer definitely was for Xpath 2.0 only.

[Arup Rakshit]

How should I write this //text()/normalize-space(.),although my one in wrong!

[mgibas]

try text()[normalize-space()]

[paul]

@MatthijsBierman where did you try? which website? I am asking so that we can try it hands on for better understanding.

[slott]

I ended up with something like this normalize-space(s:td[2]/s:a[1]/text()[1]) And that worked like a charm