How do I use buttonhole elastic?

I have a Danish sewing pattern for a maternity skirt that calls for buttonhole elastic.  The pattern just says "thread elastic through casing and fasten with a button".  There is obviously something more to it than this... I have seen a couple of tutorials online that recommend using 2 buttons, one at each end.  How much of a gap is good to leave between the buttons?  Is it better to place them in the front or the back?  With something like a maternity skirt, should you leave extra elastic on each end to allow for more stretch?

Does someone know of a good tutorial or instruction on this?  It seems like a great invention, I never heard of it until this pattern, but I have no clue really what to do with it.

Thanks!

I love buttonhole elastic for kids clothes. I only have seen it already sewn into my children's clothes. It's great. Yes, you leave 'extra' elastic because that way your child (or growing belly) will be able to wear the skirt or pants longer. If you live near a Sears I believe some of the LL Bean children's pants have the button hole elastic in them or Children's Place.

You may have to order the elastic off the internet. None of the stores by me carry it and most of them don't know what I am talking about when I ask for it.

The buttons are placed on each side on my daughter's skorts (place your hands on your hips - yup put one on each side where the seam is or a little behind it) and then the elastic is buttoned at one of the holes and can be made larger by moving the elastic down. A tip I heard from someone else (probably on this forum somewhere) was to use regular elastic as the middle and sew the button elastic onto the ends - that way you will be able to use your button elastic for more projects.

Hope this helps a bit, Beth