I need you to explain this answer.

Question 3 (18 points) Consider the following CFG for octal numbers. O +NO 0 + N +0|1|2|3|4|5|617 Augment this grammar with attribute rules that will accumulate the value of the number into a val attribute of the root of the parse tree. Solution: 01 + N 02 01.length = N.length + O2.length 01.val = N.value 802.length+ O2.val 0.length = 0 0.value = 0 N +0|1|2|3|4|5|6|7 N.value = parseInt(N) (or whatever will extract the value from a single character) N.length =1