Extended front post double crochet stitches

Dear users and authors,
What are extended front post double crochet stitches and what are they used for?

This is the first time I’ve come across “extended” front post double crochets.

I’m familiar with front post double crochets.
I sometimes use them when I want to make a crochet piece—or part of it—more three-dimensional.
By alternating them with back post double crochets, you can create cuffs.