> pww("twill", "3/2*2/1", nrow = 15, ncol = 9)
/ - - - - - - - - - \ 
| X X     X X X   X | 
| X     X X X   X X | 
|     X X X   X X   | 
|   X X X   X X     | 
| X X X   X X     X | 
| X X   X X     X X | 
| X   X X     X X X | 
|   X X     X X X   | 
| X X     X X X   X | 
| X     X X X   X X | 
|     X X X   X X   | 
|   X X X   X X     | 
| X X X   X X     X | 
| X X   X X     X X | 
| X   X X     X X X | 
\ - - - - - - - - - /