In XSLT, how come I can't set the select-attribute of a value-of using xsl:attribute, and what's a good alternative?

Question

I have a constant and a variable that I wann mouch together to select a specific node, this is what I want to do:

Answer 1

There is no runtime evaluation for XPath expression in standar XSLT 1.0

So, depending what is $inputid, you could have different solutions.

But this /root/meta/url_params/$inputid is wrong because right hand of / must be a relative path in XPath 1.0 (in XPath 2.0 can be a function call, also).

For this particulary case you can use:

/root/meta/url_params/*[name()=$inputid]

or

/root/meta/url_params/*[@id=$inputid]

For a general case, I will go with walker pattern like Dimitre's answer.