If a magic genie granted me just one formatting wish, it would be that screenwriters everywhere would understand formatting principles enough to apply them to unique situations. I'm here to help you do that. I'm your magic genie.
Actually, the issue may have less to do with knowledge and understanding, and more to do with "fear of doing the wrong thing and getting my script rejected." Believe me, I get it. There's a lot of pressure on screenwriters. First, please realize that your script does not have to be formatted perfectly. Relax and have fun when writing.
FLASHBACK - JOE'S DISASTERIOUS DATE
SERIES OF SHOTS - JOE BUYS A GUN
MONTAGE - JOE GROWS OLD
You may ask, what if it's a series of quick flashbacks one after the other? Apply the principle. Here are two solutions, both correct:
FLASHBACK MONTAGE - JOE'S CHILDHOOD
SERIES OF QUICK FLASHBACKS - JOE'S CHILDHOOD
If they're really quick, call them FLASHES if you want.
You could also have a MONTAGE OF DAYDREAMS or even A SERIES OF UNFORTUNATE EVENTS.
Let's look at some other examples of correctly formatted special scene headings.
VISION - THE END OF THE WORLD
DREAM - JOE IN THE JUNGLE
What if Joe has a mirage and you want to identify it as his? Here you go:
Notice that I didn't identify the concept, idea, or subject in this case. The principle says that I should do that when possible. If I don't do it, the reader is not going to throw the script in the trash at that moment and tear her hair out.
Now if the special situation runs for more than one scene, then the heading will be handled a little differently. For the variety of situations you can imagine, just read my article 'All About Flashbacks" or look in my book Dr. Format Tells All. You can use these sources as a guide and extrapolate from there for any special scene heading.
Cupid and narrative description
The general principle for writing action is to write what we see. This was my solution, applying the principle:
Mary sings a few bars of a popular song. A MAN jumps on stage and gives her a kiss. Happy little cupids flutter around them.
Getting the idea across
The general principle here is this: Underscore anything you want to pop out to the reader, but only a handful of times in a script.
Formatting is simpler and more flexible than we sometimes think, and one key to peace of mind when you are stuck is to look for the principles behind similar situations and see if they work for your formatting situation. If you're still stumped after looking at my books, let me know. Meanwhile, keep writing.