> pww("matt_irregular", "3/2(4+2)", nrow = 7, 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 | 
\ - - - - - - - - - / 

