Notes from the LTK pattern page:

<p>"Finally! The flirty skirty™ and the undersoaker™ bundled pattern. Boy or girl, this pattern will have you covered! With underwear-style front loading legs and a variety of leg cuff options (including rolled edge as shown above, hemmed, ribbed and picot) as well as a fully enclosed elastic waist for easy on and off (no fussing with drawstrings!)
The Flirty Skirty™ and the Undersoaker™ bundled pattern. Boy or girl, this pattern will have you covered! With underwear-style front loading legs and a variety of leg cuff options (including rolled edge as shown above, hemmed, ribbed and picot) as well as a fully enclosed elastic waist for easy on and off (no fussing with drawstrings!)

This pattern has detailed, in-depth instructions for a skirt with delicate (but easy-to-knit!) lace edge and attached undersoaker to cover diapers, and also for the undersoak on it’s own.