The command line tool I was trying to write was to read my Safari reading list on my Mac, and construct an HTML page that contains the same information that I could put on my website, where I could then access it from my Surface Pro. Apple provides a way to export the reading list in XML, so that was my input.
I don't remember what it was now, but my first approach used some XML stuff that I got out of examples from some recent C# book, and it worked fine in Visual Studio Community Edition on my Windows gaming machine. In Core, though, on my Mac (and on my Surface Pro and Windows gaming machine) it failed to build. It was not finding something I was trying to include via "using".
I was not able to figure out if that thing is simply not part of Core, or if some build setting somewhere has to be changed to make it available.
(I eventually changed my approach and dealt with the XML through LINQ instead of at a lower level, so that I no longer needed whatever it was whose "using" was giving me trouble, and successfully got access to my Reading List from my Surface Pro).
Especially since some components embedded different versions of other components.
I don't know if the situation has improved since I rotated off, but a bog-ordinary semver scheme would've saved a world of pain.
Failing that, a single page with components (SDK? Runtime?) and available version numbers that gets updated.
Because we mostly wound up working what was what from forensic readings of scattered blog posts, Github release and I think comments on Github issues.
In any case, I am sure the team would be glad to give you feedback on their experiences since then -- my email is in my profile if want me to pass anything along.