In Henning, you move the yarn to the front of your work, slip a stitch purlwise, then move the yarn to the back. Because the slipped stitch is a contrasting colour, you create a vertical stripe. You would think that slipping a stitch instead of working it for one or two rows would create tension, but actually it works quite well.
The row gauge ends up being a little compressed, but only a little. And then, because you slip the stitch with the yarn in front, the working yarn forms a horizontal strand across the contrasting vertical stripe. And that's why it looks woven!
I didn't even know about slip-stitch techniques until a couple of years ago, and read about mosaic knitting in Barbara Walker's Treasuries. You can use slipped stitches for a little bit of texture, or you can use them as the prominent motif.
Check out the trellis pattern in England Avenue Cardigan, or the mock cables in the Ferguson Cowl and Beanie. Those are made by moving slipped stitches across the surface, making a highly raised texture!
