Defining the close/end of a line_loop for the gl.mesh's index array?

I'm drawing a cube in [gen] and sending it's position array to mesh. In the end, i want the mesh to draw a wireframe cube that's not triangulated (so no diagnol/cross-lines/hypotenuses (hypoteni?). Just 12 lines, one for each edge. I'm using line_loop drawmode and can't quite figure out to close one loop and start the next one. I've tried sending the input matrix for the index array, as having a different plane for each loop (doesn't seem to like multiplanar matrices), or as having the next y-coordinate row as the beginning of the next loop (it'll just try to connect everything in a continuous line anyways).

Before i even send a new index array, gl.mesh will attempt at creating the loops, and it does create disconnected loops, so i know it's possible, I just don't know how the index array should be formatted. Is there anyway to view the gl.mesh's default index array before I set it with a new one?

In the meantime I guess I can use draw_mode lines, or quads with poly_mode 1 1. These both work fine, guess i'm just curious about line_loop.