Confused with instructions

Hi everyone. In my baby sweater pattern it says: “Dec Rows (RS): K1, k2tog, work to last 3 sts, ssk, k1.” I am now knitting the back and it says: “Side decs (RS): Work dec row every 4th row 2 times, then every other row 3 times.” My question is this: How do you decrease when the row you are working on is a purl row (St stitch). I realize I’m being really literal, but the instructions seem to indicate the decrease rows would be knit rows. Should all the decrease rows be knit rows? Or, if they are purl rows, do you decrease the same way as when you knit? And how do you ssk on a purl row? Wow! Hope you’re not as confused as I am after writing this!!
Thanks for your help!

:think: Since the RS is the decrease row I think that would mean all knitted rows…I don’t think it should be worked on a purl row…
Every 4th row:
Knit decrease Row
Purl Row (1)
Knit row (2)
Purl row (3)
Knit Decrease (4th row)
Every other row would be:
Knit row decrease
Purl row
Knit row decrease