Well, it’s just continuous text, if you have to use “cohesive”.
Multiline mode is just for viewing/editing clearly, when the term in single-line mode includes “\n” and makes one dizzy.
CTRL+ENTER is just for entering a newline character in that box. (= \n)
CTRL+ENTER is not for triggering the search.
You surely can use CTRL+ENTER at the end, if you want to search for a term that ends with a newline character(s).
In the box is just continuous text.
It’s not a list for searching 2 or more terms simultaneously.
Compare it with “Advanced Filter” feature in Filter toolbar.