The nodes of the hexagonal grid move only vertically, and are physically shifted by the various shapes (curvilinear, rectilinear, or a combination of both pushing into it from the base of the grid. The connecting lines maintain their connections, thus warping the grid.
On the left is the default hexagonal grid; the grids on the right are modified so that every other column of nodes compresses less quickly than the others, visually rendering a 'pleating effect'
Topologically, the primary rule is that none of the components (the nodes and connectors) may intersect. This poses very little limits to the default set, but puts a high amount of restriction on the pleated grids, producing interesting results.