Fabric pieces can be held apart between two layers of fine tulle which can then be stitched through.
Or holes can be cut in the middle of fabric
In the above photos I simply cut the shape away from the back behind the coloured strips but there will be a problem with fraying and I only took these photos from a design point of view.
One way I use to deal with inside raw edges of spaces is photographed below:
Lightweight iron on vilene placed glue side up on top of right side of fabric needing a space. Stitch around the shape of the hole required (I have used black thread for photographing purposes only)
Cut out inside space leaving a small seam allowance
Clip into the corners to make for easier turning
Turn the interfacing through the hole; make sure edges are 'rolled' neatly and iron interfacing down to the wrong side of the fabric.
A Quilt as You Go Method can be used to make spaces as in the image below. My method here is devious but foolproof. One day I will share this secret!
Part six of my Quilting Outside The Square series will look at squares inside spaces...