The Alternating Loop Cast On is found in RD KH on page 66.
I don’t believe there are videos online for this cast on; however it is simply done by alternating between the Loop Cast On and the Backwards Loop Cast On.
This cast on is VERY stretchy. I think the strands along the bottom in the st st portion of the swatch would work very well with a pattern that uses strands of yarn going across the right side of the fabric – such as in the Butterfly Hat or Faberge Cowl. The little hanging-down loops in the (k1, p1) section may be used as a design feature as well.