While typing in Sublime Text 3 I must have accidentally triggered some keyboard shortcut or clicked something by mistake, because suddenly I'm in some mode I can't get out of.
One function in my code is highlighted in green (or, greenish yellow):
...and there's some sort of empty copy of the function, highlighted in dark red, displayed after the highlighted function, somehow between the final line of the highlighted function and the next line:
I don't know what this mode is, or what it's called, so I can't look it up, and nothing in the "View" menu seems relevant. I've tried searching on various descriptions of it and found nothing.
What is this mode, and how do I get out of it?