What is the closing character in the next line entry?

Question

PHP

I met these entries
koi8-r''some_string_here
=?koi8-r?B?base64_string?=
Everything is clear with the second one - it started and ended
And what will be the closing character for the first type of string, if we say there will be two of them in a row
koi8-r''some string here utf-8''some string here
Will there be a single quote this symbol, or is there something else according to the standard?
Sorry, I don't know what it's called. nothing to even google. It seems not an encoding, it seems not a recording form, I don’t know