That one is the same as the M1L on the Increases page. It's a m1 knitwise; the 'pm1' is m1p, where you purl into the lifted strand. It's the same only you're supposed to insert the left needle from front to back and purl through the back loop. It's actually easier to insert the needle the same as the knit, from back to front, and purl into the front loop. The idea is to twist the yarn loop so it doesn't leave a hole.