before:
@- = (0)		 1 items
@+ = (0, , , , , )	 6 items

expr:
@- = (0, , , , 0, 1)	 6 items
@+ = (2, , , , 1, 2)	 6 items

expr:
@- = (0, 0, , , 2, 3)	 6 items
@+ = (4, 2, , , 3, 4)	 6 items

after:
@- = (0, 0, 2)		 3 items
@+ = (4, 2, 4, , , )	 6 items

matches: (abcd)
At the very end:
@- = (0, 0, 2)	 3 items
@+ = (4, 2, 4, , , )	 6 items