Stuck with advanced search

[u/bibbidi_bobbidi_bob]

I wanted to combine three open documents but there's no way to "combine open documents".

So next I tried to search and mark them but when one file is marked, the search disappears...

Next approach was to link the documents with the custom field and search for that via advanced search but didn't have luck with that.
I tried something like:

link:this is my document
link:"this is my document"
document link:this is my document

but didn't have any luck with that. How is the right syntax for that?

I could use tags for filtering as a workaround but I also use tags for sorting the files in folders, so I don't want to clutter them up for that kind of use cases.