So it turned out you were not really searching for multip-line strings…

No need to use that Multiline mode unless you want to match a multi-line string.

That box in Multiline mode is not a “list”, if you thought it was.

If the above is enough to answer the last question, don’t read further in case you will be confused again. ;)

As for Multiline mode with search options:

If you turn on “Multiline” with “(None)”, only exact-text searches can be done.
e.g. in Find box:
only matches as a whole:

However, EmEditor does such a search using “Escape Sequence” internally.
The expression is saved as “2\n3\n4”. And if you turn off “Multiline”, “Escape Sequence” will be turned on automatically.

So, to search for a multi-line string,
either you always use Multiline mode with “(None)” to do an exact-text search,
or, turn on “Escape Sequence” at least and use “\n”.

Escape Sequence syntax is very simple. See it in the menu of the “>” button.
A common text search only needs \n \t \\ when necessary.

Use Regular Expressions if the content/length of the matches is uncertain.

>… are marked in green.

EmEditor cannot highlight multi-line matches with colors.
A match will be highlighted with colors unless it’s multi-line.