argument to row query

Hi!
Great module!
It solved integrating large datasets from large xml files from important sources to our university :)
however, to get it to solve my use case I had to create a patch. Maybe this patch contains something useful for others?
This is my first attempt at contributing a patch, so maybe you will only find the ideas described here useful, if at all :)

I tried the argument filter from #1429516: Add argument support → , but it seems to me it filters on the already chosen rows from the xpath row query? In the case I had to solve, selecting all rows and then filtering meant the solution seemed slow.

I see there is another feature request with patches already for altering the query settings, ✨ URL as an argument Closed: won't fix , however it seems to me this feature request and patch solves passing arguments to the source url of the xml file. I found a variant on this approach to pass arguments to the xpath query this way:

Given this xpath:
with an argument of M-MP:
/topelement/studyprogram/studyprogramcode[text()="M-MP"]/parent::studyprogram/topic

This selects all topics in one studyprogram from our catalogue and makes the presentation of this program much faster.
It also allows for faster searching. (for instance with argument searching from the above patch.

Using the attached patch applied to 7.x-1.0-alpha4 I succeeded in passing arguments via url to the xpath row query.
Maybe theres an alternat approach here, without programming - but I found only the suggested solution.

Thanks for your contributions!