Question

So I’ve been working on some XSLT to modify YouTube’s RSS XML, and of course as soon as I got it working, they’ve changed their formatting. Before, each video’s unique ID was stored between <videoid> tags, which you could then use to create a URL. But now the only way to get a video’s URL is from a tag like this

<media:player url='https://www.youtube.com/watch?v=XXXXXXXXXXX&amp;feature=youtube_gdata_player'/>`

which is contained within <media:group> tags.

The way I’ve been trying to get at it is

<xsl:value-of select="media:group/media:player@url" />

but doing that gives me a compilation error that says

xsl:value-of : could not compile select expression 'media:group/media:player@url'

Does anyone see anything wrong with that?

Also, as a side note, I want to do something similar with

<xsl:value-of select="media:group/media:thumbnail@url" />

however there are several <media:thumbnail> tags for each entry; would this just grab the first one, or would this potentially cause errors?

Answer 1

you are missing a / in your XPath. Try:

<xsl:value-of select="media:group/media:player/@url" />

As far as DOM API is concerned, attributes belong to an element. The XPath goes about it in a slightly different way. Child nodes live on the child:: axes (which is the default so you rarely see it used explicitly) and attributes live on the atribute:: axes (you can get there with the abbreviated @). When constructing an XPath expression you are basically building a sequence of location steps separated by /. An attribute is “one location step” away from the element owning it.

To the second part of your question. The selector will create a sequence (think node list) of all nodes that match the expression and will do what the xsl: instruction prescribes to do on that sequence. In your case (xsl:value-of), all @url of all matching media:thumbnail will be put together in a node-set that will be further converted to a string:

A node-set is converted to a string by returning the string-value of the node in the node-set that is first in document order

So you will get the value of the “first” one. That said, I would argue that running xsl:value-of on a sequence of more than one node is not really intuitive (even though the spec clearly says what it will do) so you would do a favor to someone reading the code after you if you be more specific with your selectors. Something like: media:group/media:thumbnail[1]/@url