Summer & Winter is a tied weave

Summer & Winter is a "tied" weave.  This class of weaves is called so because some of the warps act as "tie-downs" to keep the pattern wefts from forming "floats" that are too long over the surface of the cloth.

In this picture I've thrown a pattern weft without tie-down warps raised.  You can see the long floats that are formed.  This will not make a practical cloth; these floats would get caught and pull out of shape.

In this next photo, I've taken that "wrong" shot of weft back out, and thrown it again with tie-down warps raised correctly.  The pattern weft still sits on top of the lighter ground weave, but it is held nicely in place by the tie-down warps.