Writing in Dual Dialogue uses the caret (^) to signal when a line should pair up with the line that comes before it.
For example, this section of Greta Gerwig’s script for Little Women looks like this on the page:
And would look like this in Highland 2:
LAURIE AMY! You’re so /grown up! AMY^ /You wrote you’d come to the hotel! LAURIE I looked for you and couldn’t find /you anywhere! AMY^ /You didn’t look hard enough! LAURIE Maybe I just didn’t recognize you, you’ve become so beaut/iful. AMY^ (making a face) /Please don’t.